fix: Sync-Icon nur während aktiver Synchronisation animieren

Die Drehung hing an der Queue-Länge statt am laufenden Sync. Veraltete
Queue-Einträge werden nach Pull bereinigt; parallele syncAll-Läufe
werden im Sync-State korrekt gezählt.

Co-authored-by: Cursor <cursoragent@cursor.com>

client/src/hooks/useSyncIndicator.ts

@@ -0,0 +1,28 @@
+import { useEffect, useState } from 'react'
+import { useLiveQuery } from 'dexie-react-hooks'
+import { db } from '../services/db.js'
+import { subscribeToSyncState } from '../services/sync.js'
+
+/** Sync queue depth and whether a sync pass is running (for header indicators). */
+export function useSyncIndicator(logbookId?: string | null) {
+  const [isSyncing, setIsSyncing] = useState(false)
+
+  const pendingCount =
+    useLiveQuery(
+      () =>
+        logbookId
+          ? db.syncQueue.where({ logbookId }).count()
+          : db.syncQueue.count(),
+      [logbookId]
+    ) ?? 0
+
+  useEffect(() => subscribeToSyncState(setIsSyncing), [])
+
+  return {
+    isSyncing,
+    pendingCount,
+    /** Spin only while a sync pass is active — not for stale queue counts. */
+    showSpinner: isSyncing,
+    showPendingWarning: pendingCount > 0 && !isSyncing
+  }
+}