feat(PROJ-52): Vollständigkeits-Reconciliation (Zähl-Report Mailserver vs. Archiv)

Täglicher Cron-Job (archivmail reconcile) berechnet pro Tenant/Quelle
(SMTP-Journal, IMAP-Konto, POP3-Konto, Datei-Import) archivierte Mail-Zahlen,
für IMAP zusätzlich einen Soll/Ist-Vergleich via UID-Tracking. Abweichungen
über Schwellenwert erzeugen Audit-Log-Warnung. Neue Admin-Dashboard-Kachel
"Vollständigkeits-Check" (letzte 7 Tage, Warn-Badge, CSV-Export).

Schließt die "teilweise erfüllt"-Lücke bei Vollständigkeit im
GoBD/DSGVO-Compliance-Check (VOI-Grundsatz 2).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

config/config.docker.yml.example

@@ -91,5 +91,12 @@ audit:
   log_path:       /var/archivmail/audit.log
   retention_days: 365
 
+# PROJ-52: Vollständigkeits-Reconciliation (Zähl-Report Mailserver vs. Archiv).
+# Täglich per Cron ausführen: `archivmail reconcile` (rechnet den Vortag ab).
+# alert_threshold_pct = relativer Rückgang (%) unter den 7-Tage-Durchschnitt,
+# ab dem ein reconciliation_anomaly Audit-Eintrag entsteht (Default 50).
+# reconciliation:
+#   alert_threshold_pct: 50
+
 logging:
   level: info

config/config.go

@@ -42,6 +42,39 @@ type Config struct {
 	// PROJ-56: load-spreading for background jobs.
 	OCR           OCRConfig           `yaml:"ocr"`
 	IMAPScheduler IMAPSchedulerConfig `yaml:"imap_scheduler"`
+	// PROJ-52: Vollständigkeits-Reconciliation (Zähl-Report Mailserver vs. Archiv).
+	Reconciliation ReconciliationConfig `yaml:"reconciliation"`
+}
+
+// ReconciliationConfig holds settings for the daily completeness reconciliation
+// job (PROJ-52). The job counts newly archived mails per source and per day and
+// flags significant drops against the trailing 7-day average.
+type ReconciliationConfig struct {
+	// AlertThresholdPct is the relative drop (in percent, below the trailing
+	// 7-day average) that triggers a `reconciliation_anomaly` audit entry.
+	// A pointer so an explicit 0 (alert on any drop) is distinguishable from an
+	// unset value (use the default).
+	//   nil -> DefaultReconciliationThresholdPct (50%)
+	//   0   -> alert whenever today's count is below the average
+	//   1..100 -> alert when today's count is more than this % below the average
+	AlertThresholdPct *int `yaml:"alert_threshold_pct,omitempty"`
+}
+
+// DefaultReconciliationThresholdPct is the default drop threshold (50% below the
+// trailing 7-day average) applied when reconciliation.alert_threshold_pct is
+// omitted from the config.
+const DefaultReconciliationThresholdPct = 50
+
+// ResolvedThresholdPct returns the effective alert threshold in percent.
+// A nil or out-of-range value falls back to the default.
+func (c ReconciliationConfig) ResolvedThresholdPct() int {
+	if c.AlertThresholdPct == nil {
+		return DefaultReconciliationThresholdPct
+	}
+	if *c.AlertThresholdPct < 0 || *c.AlertThresholdPct > 100 {
+		return DefaultReconciliationThresholdPct
+	}
+	return *c.AlertThresholdPct
 }
 
 // OCRConfig holds settings for the background OCR worker (PROJ-56).