feat: Überstunden-Kappung + Jahresverfall pro Firma konfigurierbar

Backend:
- Company: overtime_cap_hours, overtime_expiry_enabled/month/day,
  overtime_max_carryover_hours
- OvertimeBalance: last_expiry_applied_at
- Migration 0031: neue Spalten in companies + overtime_balances
- _recalculate_overtime_balance: Kappung direkt nach Berechnung
- apply_overtime_expiry_if_needed(): lazy Verfall beim Balance-Abruf
- GET /absences/overtime-balance: prüft + wendet Verfall automatisch an
- POST /absences/overtime-balance/apply-expiry: manueller Trigger (Admin)

Frontend:
- CompanySettingsPage: neuer Block 'Überstunden-Konto'
  - Toggle Kappungsgrenze + Stunden-Input
  - Toggle Jahresverfall + Stichtag (Tag/Monat) + max. Übertrag
  - 'Verfall anwenden'-Button für Admins

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/CompanySettingsPage.tsx

@@ -62,6 +62,14 @@ export function CompanySettingsPage() {
   // Freizeitausgleich
   const [fzaOverdraftAllowed, setFzaOverdraftAllowed] = useState(true)
   const [fzaWarningThreshold, setFzaWarningThreshold] = useState(0)
+  // Überstunden-Kappung
+  const [overtimeCapEnabled, setOvertimeCapEnabled] = useState(false)
+  const [overtimeCapHours, setOvertimeCapHours] = useState(150)
+  // Überstunden-Verfall
+  const [overtimeExpiryEnabled, setOvertimeExpiryEnabled] = useState(false)
+  const [overtimeExpiryMonth, setOvertimeExpiryMonth] = useState(3)
+  const [overtimeExpiryDay, setOvertimeExpiryDay] = useState(31)
+  const [overtimeMaxCarryoverHours, setOvertimeMaxCarryoverHours] = useState<number | null>(null)
   // Busylight
   const [blStatus, setBlStatus] = useState<{ configured: boolean; created_at: string | null } | null>(null)
   const [blPlaintext, setBlPlaintext] = useState<string | null>(null)
@@ -85,13 +93,19 @@ export function CompanySettingsPage() {
       setPnRequired(c.personnel_number_required ?? false)
       setPnMode(c.personnel_number_mode ?? 'manual')
       setPnNext(c.personnel_number_next ?? 1)
-      const cc = c as CompanyOut & { mobile_stamping_enabled?: boolean; overtime_overdraft_allowed?: boolean; overtime_warning_threshold_hours?: number; kiosk_require_approval?: boolean; kiosk_track_current_user?: boolean; kiosk_heartbeat_interval_sec?: number }
+      const cc = c as CompanyOut & { mobile_stamping_enabled?: boolean; overtime_overdraft_allowed?: boolean; overtime_warning_threshold_hours?: number; kiosk_require_approval?: boolean; kiosk_track_current_user?: boolean; kiosk_heartbeat_interval_sec?: number; overtime_cap_hours?: number | null; overtime_expiry_enabled?: boolean; overtime_expiry_month?: number; overtime_expiry_day?: number; overtime_max_carryover_hours?: number | null }
       setMobileStamping(cc.mobile_stamping_enabled ?? true)
       setFzaOverdraftAllowed(cc.overtime_overdraft_allowed ?? true)
       setFzaWarningThreshold(cc.overtime_warning_threshold_hours ?? 0)
       setKioskRequireApproval(cc.kiosk_require_approval ?? true)
       setKioskTrackCurrentUser(cc.kiosk_track_current_user ?? true)
       setKioskHeartbeatIntervalSec(cc.kiosk_heartbeat_interval_sec ?? 30)
+      setOvertimeCapEnabled(cc.overtime_cap_hours != null)
+      setOvertimeCapHours(cc.overtime_cap_hours ?? 150)
+      setOvertimeExpiryEnabled(cc.overtime_expiry_enabled ?? false)
+      setOvertimeExpiryMonth(cc.overtime_expiry_month ?? 3)
+      setOvertimeExpiryDay(cc.overtime_expiry_day ?? 31)
+      setOvertimeMaxCarryoverHours(cc.overtime_max_carryover_hours ?? null)
     }).catch(() => {})
     api.get<{ configured: boolean; created_at: string | null }>('/companies/me/busylight-token')
       .then(setBlStatus)
@@ -165,6 +179,11 @@ export function CompanySettingsPage() {
         kiosk_require_approval: kioskRequireApproval,
         kiosk_track_current_user: kioskTrackCurrentUser,
         kiosk_heartbeat_interval_sec: kioskHeartbeatIntervalSec,
+        overtime_cap_hours: overtimeCapEnabled ? overtimeCapHours : null,
+        overtime_expiry_enabled: overtimeExpiryEnabled,
+        overtime_expiry_month: overtimeExpiryMonth,
+        overtime_expiry_day: overtimeExpiryDay,
+        overtime_max_carryover_hours: overtimeExpiryEnabled ? overtimeMaxCarryoverHours : null,
       })
       setCompany(updated)
       setSaved(true)
@@ -176,6 +195,18 @@ export function CompanySettingsPage() {
     }
   }
 
+  async function applyOvertimeExpiry() {
+    if (!confirm('Verfall jetzt auf alle Mitarbeiter anwenden? Nicht rückgängig zu machen.')) return
+    try {
+      await api.post('/absences/overtime-balance/apply-expiry', {})
+      setError(null)
+      setSaved(true)
+      setTimeout(() => setSaved(false), 3000)
+    } catch (e: unknown) {
+      setError(e instanceof Error ? e.message : 'Fehler beim Anwenden des Verfalls')
+    }
+  }
+
   const isAdmin = me?.role === 'COMPANY_ADMIN' || me?.role === 'SUPER_ADMIN'
 
   const hourOptions = Array.from({ length: 24 }, (_, i) => i.toString())
@@ -699,6 +730,134 @@ export function CompanySettingsPage() {
           </div>
         </div>
 
+        {/* Überstunden-Konto-Regeln */}
+        <div className="bg-white rounded-xl shadow-sm border border-gray-200 p-6 space-y-5">
+          <div className="flex items-center gap-2">
+            <span className="text-lg">📊</span>
+            <h2 className="font-semibold text-gray-700">Überstunden-Konto</h2>
+          </div>
+
+          {/* Kappungsgrenze */}
+          <div className="space-y-3">
+            <div className="flex items-center justify-between gap-4">
+              <div>
+                <p className="text-sm font-medium text-gray-800">Kappungsgrenze aktivieren</p>
+                <p className="text-xs text-gray-500 mt-0.5">
+                  Das Überstunden-Konto kann nicht über diesen Wert anwachsen.
+                </p>
+              </div>
+              <button
+                type="button"
+                disabled={!isAdmin}
+                onClick={() => setOvertimeCapEnabled(v => !v)}
+                className={`relative inline-flex h-6 w-11 flex-shrink-0 rounded-full border-2 border-transparent transition-colors duration-200 focus:outline-none disabled:opacity-50 disabled:cursor-not-allowed ${
+                  overtimeCapEnabled ? 'bg-blue-600' : 'bg-gray-300'
+                }`}
+              >
+                <span
+                  className={`pointer-events-none inline-block h-5 w-5 rounded-full bg-white shadow transform transition-transform duration-200 ${
+                    overtimeCapEnabled ? 'translate-x-5' : 'translate-x-0'
+                  }`}
+                />
+              </button>
+            </div>
+            {overtimeCapEnabled && (
+              <div className="flex items-center justify-between gap-4 pl-4 border-l-2 border-blue-100">
+                <p className="text-sm text-gray-700">Maximale Überstunden (Stunden)</p>
+                <input
+                  type="number" min={1} max={9999} step={1}
+                  value={overtimeCapHours}
+                  onChange={e => setOvertimeCapHours(Math.max(1, parseInt(e.target.value) || 1))}
+                  disabled={!isAdmin}
+                  className="w-24 border border-gray-300 rounded-lg px-3 py-1.5 text-sm text-right disabled:bg-gray-50"
+                />
+              </div>
+            )}
+          </div>
+
+          {/* Verfall */}
+          <div className="space-y-3">
+            <div className="flex items-center justify-between gap-4">
+              <div>
+                <p className="text-sm font-medium text-gray-800">Jahresverfall aktivieren</p>
+                <p className="text-xs text-gray-500 mt-0.5">
+                  Nicht genommene Überstunden verfallen einmal jährlich zum konfigurierten Stichtag.
+                </p>
+              </div>
+              <button
+                type="button"
+                disabled={!isAdmin}
+                onClick={() => setOvertimeExpiryEnabled(v => !v)}
+                className={`relative inline-flex h-6 w-11 flex-shrink-0 rounded-full border-2 border-transparent transition-colors duration-200 focus:outline-none disabled:opacity-50 disabled:cursor-not-allowed ${
+                  overtimeExpiryEnabled ? 'bg-blue-600' : 'bg-gray-300'
+                }`}
+              >
+                <span
+                  className={`pointer-events-none inline-block h-5 w-5 rounded-full bg-white shadow transform transition-transform duration-200 ${
+                    overtimeExpiryEnabled ? 'translate-x-5' : 'translate-x-0'
+                  }`}
+                />
+              </button>
+            </div>
+            {overtimeExpiryEnabled && (
+              <div className="pl-4 border-l-2 border-blue-100 space-y-3">
+                {/* Stichtag */}
+                <div className="flex items-center justify-between gap-4">
+                  <p className="text-sm text-gray-700">Verfallsstichtag</p>
+                  <div className="flex items-center gap-2">
+                    <input
+                      type="number" min={1} max={31} step={1}
+                      value={overtimeExpiryDay}
+                      onChange={e => setOvertimeExpiryDay(Math.min(31, Math.max(1, parseInt(e.target.value) || 1)))}
+                      disabled={!isAdmin}
+                      className="w-16 border border-gray-300 rounded-lg px-2 py-1.5 text-sm text-right disabled:bg-gray-50"
+                    />
+                    <span className="text-sm text-gray-500">.</span>
+                    <select
+                      value={overtimeExpiryMonth}
+                      onChange={e => setOvertimeExpiryMonth(parseInt(e.target.value))}
+                      disabled={!isAdmin}
+                      className="border border-gray-300 rounded-lg px-2 py-1.5 text-sm disabled:bg-gray-50"
+                    >
+                      {['Jan','Feb','Mär','Apr','Mai','Jun','Jul','Aug','Sep','Okt','Nov','Dez'].map((m,i) => (
+                        <option key={i+1} value={i+1}>{m}</option>
+                      ))}
+                    </select>
+                  </div>
+                </div>
+                {/* Max. Übertrag */}
+                <div className="flex items-center justify-between gap-4">
+                  <div>
+                    <p className="text-sm text-gray-700">Maximaler Übertrag (Stunden)</p>
+                    <p className="text-xs text-gray-400">0 = alles verfällt · leer = alles übertragen</p>
+                  </div>
+                  <input
+                    type="number" min={0} max={9999} step={1}
+                    value={overtimeMaxCarryoverHours ?? ''}
+                    placeholder="unbegrenzt"
+                    onChange={e => setOvertimeMaxCarryoverHours(e.target.value === '' ? null : Math.max(0, parseInt(e.target.value) || 0))}
+                    disabled={!isAdmin}
+                    className="w-28 border border-gray-300 rounded-lg px-3 py-1.5 text-sm text-right disabled:bg-gray-50 placeholder-gray-400"
+                  />
+                </div>
+                {/* Manueller Trigger */}
+                {isAdmin && (
+                  <div className="flex items-center justify-between gap-4 pt-1">
+                    <p className="text-xs text-gray-500">Verfall jetzt auf alle Mitarbeiter anwenden</p>
+                    <button
+                      type="button"
+                      onClick={applyOvertimeExpiry}
+                      className="px-3 py-1.5 text-xs font-medium bg-orange-50 border border-orange-200 text-orange-700 rounded-lg hover:bg-orange-100 transition-colors"
+                    >
+                      Verfall anwenden
+                    </button>
+                  </div>
+                )}
+              </div>
+            )}
+          </div>
+        </div>
+
         {/* Firmen-Info (readonly) */}
         {company && (
           <div className="bg-white rounded-xl shadow-sm border border-gray-200 p-6">