fix(imap): IMAP/POP3-Import in korrekten Tenant-Index schreiben

IMAP- und POP3-Importer haben Mails immer nur in emails_global
indexiert (TenantID nie gesetzt, idxMgr.Global() statt
ForTenant(tenantID)). Dadurch fehlten neue Mails ab dem letzten
Server-Neustart im Tenant-Index (Suche zeigte veraltete Ergebnisse).

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

internal/pop3/importer.go

@@ -16,7 +16,7 @@ import (
 type Importer struct {
 	store     *Store
 	mailStore *storage.Store
-	idx       index.Indexer
+	idxMgr    index.TenantIndexer
 	logger    *slog.Logger
 	TenantID  *int64 // optional tenant assignment for stored mails
 	// PROJ-44: optional OCR enqueue hook, wired from main.go.
@@ -24,11 +24,11 @@ type Importer struct {
 }
 
 // NewImporter creates a new Importer wired to the storage and index backends.
-func NewImporter(store *Store, mailStore *storage.Store, idx index.Indexer, logger *slog.Logger) *Importer {
+func NewImporter(store *Store, mailStore *storage.Store, idxMgr index.TenantIndexer, logger *slog.Logger) *Importer {
 	return &Importer{
 		store:     store,
 		mailStore: mailStore,
-		idx:       idx,
+		idxMgr:    idxMgr,
 		logger:    logger,
 	}
 }
@@ -167,9 +167,10 @@ func (imp *Importer) storeAndIndex(raw []byte, log *slog.Logger) error {
 		HasAttachment: len(pm.Attachments) > 0,
 		Date:          pm.Date,
 		Size:          int64(len(raw)),
+		TenantID:      imp.TenantID,
 	}
 
-	if err := imp.idx.IndexSync(doc); err != nil {
+	if err := imp.idxMgr.ForTenant(imp.TenantID).IndexSync(doc); err != nil {
 		log.Warn("failed to index mail", "id", id, "err", err)
 		// Non-fatal: mail is stored, just not searchable yet
 	}