refactor: rename project to winnow

- Rename Python package directory if_curator/ → winnow/
- Update all imports, entry points, and CLI references
- Update pyproject.toml: name, scripts, package list, repository URL
- Update Dockerfile, compose.yml, entrypoint.sh, scheduler.py
- Update GitHub Actions workflow image names
- Update README

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

entrypoint.sh

@@ -4,7 +4,7 @@ export PYTHONUNBUFFERED=1
 
 # 1. Run the job immediately on startup
 echo "▶ Running on startup..."
-uv run python -m if_curator.cli
+uv run python -m winnow.cli
 
 # 2. If a schedule exists, start the scheduler
 if [ -n "${CRON_SCHEDULE:-}" ]; then