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>

docker-compose.yml

@@ -25,8 +25,6 @@ services:
       VAPID_PRIVATE_KEY: "${VAPID_PRIVATE_KEY:-}"
       VAPID_PUBLIC_KEY: "${VAPID_PUBLIC_KEY:-}"
       VAPID_CLAIMS_SUB: "${VAPID_CLAIMS_SUB:-mailto:admin@fabledassistant.local}"
-      # Prevent HuggingFace from making network calls at startup once models are cached:
-      HF_HUB_OFFLINE: "${HF_HUB_OFFLINE:-0}"
     healthcheck:
       test: ["CMD", "python", "-c", "import urllib.request; urllib.request.urlopen('http://localhost:5000/api/health')"]
       interval: 10s