feat(PROJ-25): User-Profil & Einstellungen — Passwort, E-Mail, 2FA

Backend:
- PATCH /api/auth/password — Passwort ändern (bcrypt, LDAP-Guard, Audit-Log)
- PATCH /api/auth/email — E-Mail ändern (Unique-Check, LDAP-Guard, Audit-Log)
- userstore: UpdatePassword, UpdateEmail, GetPasswordHash

Frontend:
- UserNav.tsx: Dropdown-Menü (Profil & Einstellungen, Abmelden)
- navbar.tsx: UserNav eingebunden
- /settings: Passwort ändern, E-Mail ändern, 2FA verwalten (QR-Code + Deaktivieren)
- api.ts: changePassword, changeEmail, getTOTPSetup, confirmTOTPSetup, disableTOTP

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

src/components/UserNav.tsx

@@ -0,0 +1,60 @@
+"use client";
+
+import { useRouter } from "next/navigation";
+import {
+  DropdownMenu,
+  DropdownMenuContent,
+  DropdownMenuItem,
+  DropdownMenuSeparator,
+  DropdownMenuTrigger,
+} from "@/components/ui/dropdown-menu";
+import { Button } from "@/components/ui/button";
+import { Badge } from "@/components/ui/badge";
+import { ChevronDown } from "lucide-react";
+import { logout } from "@/lib/api";
+
+interface UserNavProps {
+  username: string;
+  role: string;
+}
+
+export function UserNav({ username, role }: UserNavProps) {
+  const router = useRouter();
+
+  async function handleLogout() {
+    try {
+      await logout();
+    } catch {
+      // ignore logout errors
+    }
+    router.push("/");
+  }
+
+  return (
+    <DropdownMenu>
+      <DropdownMenuTrigger asChild>
+        <Button
+          variant="ghost"
+          size="sm"
+          className="flex items-center gap-2"
+          aria-label="Benutzermenu"
+        >
+          <span className="text-sm font-medium">{username}</span>
+          <Badge variant="secondary" className="text-xs">
+            {role}
+          </Badge>
+          <ChevronDown className="h-4 w-4 opacity-50" />
+        </Button>
+      </DropdownMenuTrigger>
+      <DropdownMenuContent align="end" className="w-48">
+        <DropdownMenuItem onClick={() => router.push("/settings")}>
+          Profil &amp; Einstellungen
+        </DropdownMenuItem>
+        <DropdownMenuSeparator />
+        <DropdownMenuItem onClick={handleLogout} className="text-red-600">
+          Abmelden
+        </DropdownMenuItem>
+      </DropdownMenuContent>
+    </DropdownMenu>
+  );
+}