feat(versions): daily 03:00 UTC auto-pin scan scheduler

BackgroundScheduler with a single CronTrigger fires scan_all_users_for
_auto_pins via asyncio.run_coroutine_threadsafe (mirrors the journal-
scheduler pattern). Wired into app startup/shutdown alongside the other
schedulers.

src/fabledassistant/app.py

@@ -331,6 +331,12 @@ def create_app() -> Quart:
         from fabledassistant.services.event_scheduler import start_event_scheduler
         start_event_scheduler(asyncio.get_running_loop())
 
+        # Start version-pinning scheduler (daily auto-pin scan at 03:00 UTC)
+        from fabledassistant.services.version_pinning_scheduler import (
+            start_version_pinning_scheduler,
+        )
+        start_version_pinning_scheduler(asyncio.get_running_loop())
+
         # Voice model loading (enabled via Admin → Config in the UI, or VOICE_ENABLED env var)
         from fabledassistant.services.stt import load_stt_model
         from fabledassistant.services.tts import load_tts_model
@@ -343,6 +349,10 @@ def create_app() -> Quart:
         stop_journal_scheduler()
         from fabledassistant.services.event_scheduler import stop_event_scheduler
         stop_event_scheduler()
+        from fabledassistant.services.version_pinning_scheduler import (
+            stop_version_pinning_scheduler,
+        )
+        stop_version_pinning_scheduler()
 
     @app.route("/")
     async def serve_index():