fix: INSIGHTFACE_HOME path, entrypoint, caching default, CRON_SCHEDULE opt-in

- Dockerfile: ENV INSIGHTFACE_HOME=/models → /models/.insightface to
  match compose.yml and .env.example; the old value caused InsightFace
  to store models at /models/models/buffalo_l (double-appended subdir)
- entrypoint.sh: use /app/.venv/bin/winnow (installed entry point)
  instead of python -m winnow.cli
- config.py: ENABLE_CACHE default false → true; embedding cache is
  always beneficial in practice; users can opt out with ENABLE_CACHE=false
- compose.yml: comment out CRON_SCHEDULE so scheduling is opt-in;
  flip ENABLE_CACHE to commented opt-out to reflect new default
- README.md: update ENABLE_CACHE default documentation to true
- tests/test_config.py: update default assertion to match

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

Dockerfile

@@ -71,7 +71,7 @@ RUN groupadd -g 568 apps && useradd -u 568 -g apps -m -s /bin/bash appuser \
 
 WORKDIR /app
 USER appuser
-ENV HF_HOME=/models/huggingface INSIGHTFACE_HOME=/models
+ENV HF_HOME=/models/huggingface INSIGHTFACE_HOME=/models/.insightface
 
 HEALTHCHECK CMD test -f /app/entrypoint.sh || exit 1
 ENTRYPOINT ["tini", "--", "/app/entrypoint.sh"]