fix: make face_mesh model pre-download non-fatal during build

Network restrictions in HF build env can block Google Storage.
The app will retry the download at startup if it fails here.

Dockerfile

@@ -63,7 +63,12 @@ print('Checkpoint resolution done')\
 RUN npm install && npm run build && mkdir -p /app/static && cp -R dist/* /app/static/
 
 ENV FOCUSGUARD_CACHE_DIR=/app/.cache/focusguard
-RUN python -c "from models.face_mesh import _ensure_model; _ensure_model()"
+RUN python -c "\
+try:\
+  from models.face_mesh import _ensure_model; _ensure_model(); print('face_mesh model cached')\
+except Exception as e:\
+  print(f'face_mesh pre-download skipped: {e} — will retry at runtime')\
+"
 
 RUN mkdir -p /app/data && chown -R user:user /app