feat(PROJ-30): Xapian → Manticore Search Migration

- internal/index/manticore.go: ManticoreTenantManager + manticoreIndex (RT-Indizes, CGO-frei)
- internal/index/index.go: TenantIndexer Interface (Xapian + Manticore)
- internal/index/tenant_worker.go: mgr-Typ auf TenantIndexer Interface
- internal/api/server.go: idxMgr auf TenantIndexer Interface
- config/config.go: IndexConfig.ManticoreDSN Feld
- cmd/archivmail/cmd_reindex.go: reindex Subkommando
- cmd/archivmail/main.go: Manticore-Branch + reindex Case
- go.mod: github.com/go-sql-driver/mysql v1.8.1
- update.sh: Manticore auto-install, CGO_ENABLED=0, config.yml migration, auto-reindex

fix(IMAP): TCP-Deadline-Wrapper für steckengebliebene Imports
fix(auth): Email-Claim in JWT für User-Isolation
fix(search): User-Isolation via sess.Email (fail-safe)
fix(ui): Admin-Login Auth-Cache, Logout-Redirect, IMAP-Polling-Resilienz

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

internal/imap/scheduler.go

@@ -207,7 +207,7 @@ func (s *Scheduler) doSync(ctx context.Context, accountID int64) (int, uint32, e
 		return 0, 0, fmt.Errorf("imap scheduler: login: %w", err)
 	}
 
-	folders, err := ListFolders(c)
+	folders, err := ListFolders(c.Client)
 	if err != nil {
 		return 0, 0, fmt.Errorf("imap scheduler: list folders: %w", err)
 	}
@@ -247,7 +247,7 @@ func (s *Scheduler) doSync(ctx context.Context, accountID int64) (int, uint32, e
 // syncFolder syncs new messages from a single IMAP folder.
 func (s *Scheduler) syncFolder(
 	ctx context.Context,
-	c *imapclient.Client,
+	c *Conn,
 	acc *Account,
 	folder string,
 	log *slog.Logger,
@@ -298,7 +298,9 @@ func (s *Scheduler) syncFolder(
 		}
 		batch := uids[i:end]
 
-		count, batchMaxUID, err := s.fetchSyncBatch(c, batch, log)
+		c.SetFetchDeadline()
+		count, batchMaxUID, err := s.fetchSyncBatch(c.Client, batch, acc.TenantID, log)
+		c.ClearDeadline()
 		if err != nil {
 			log.Warn("imap scheduler: batch error, continuing",
 				"folder", folder, "offset", i, "err", err)
@@ -320,6 +322,7 @@ func (s *Scheduler) syncFolder(
 func (s *Scheduler) fetchSyncBatch(
 	c *imapclient.Client,
 	uids []imapv2.UID,
+	tenantID *int64,
 	log *slog.Logger,
 ) (int, uint32, error) {
 	if len(uids) == 0 {
@@ -367,7 +370,7 @@ func (s *Scheduler) fetchSyncBatch(
 			}
 
 			if len(raw) > 0 {
-				if err := s.importer.storeAndIndex(raw, log); err != nil {
+				if err := s.importer.storeAndIndex(raw, tenantID, log); err != nil {
 					log.Warn("imap scheduler: store/index failed", "err", err)
 				} else {
 					imported++