feat: automatic Kokoro offline mode + daily update check

- On first load: model runs online (downloads .pt files), then stores the
  current HF commit SHA to /data/kokoro_commit_hash.txt and switches the
  process to offline mode (HF_HUB_OFFLINE) for all future requests
- On subsequent restarts: presence of the commit file triggers offline mode
  before the pipeline loads, skipping all HuggingFace network validation
- Daily at 03:00 UTC: scheduler temporarily lifts offline mode, fetches the
  latest commit SHA from HF, and only reloads the pipeline if the model has
  actually changed — then restores offline mode
- Removed HF_HUB_OFFLINE from docker-compose.yml; behaviour is now automatic
  and not a hoster/user concern

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

src/fabledassistant/services/briefing_scheduler.py

@@ -343,6 +343,21 @@ async def start_briefing_scheduler(loop: asyncio.AbstractEventLoop) -> None:
         replace_existing=True,
     )
 
+    def _run_kokoro_update_check() -> None:
+        from fabledassistant.services.tts import check_for_kokoro_updates
+        future = asyncio.run_coroutine_threadsafe(check_for_kokoro_updates(), _loop)
+        try:
+            future.result(timeout=300)
+        except Exception as exc:
+            logger.error("Kokoro update check failed: %s", exc)
+
+    _scheduler.add_job(
+        _run_kokoro_update_check,
+        CronTrigger(hour=3, minute=0, timezone="UTC"),
+        id="kokoro_update_check_daily",
+        replace_existing=True,
+    )
+
     _scheduler.start()
     logger.info(
         "Briefing scheduler started with %d user(s) across %d job(s)",