refactor: split data/ into ephe/ and cache/
- data/ephe/: static Swiss Ephemeris .se1 files, git-tracked, copied into Docker image
- data/cache/: runtime sqlite cache (ephemeris.sqlite3), gitignored
- Update config.py: DATA_DIR -> data/ephe, DB_PATH -> data/cache/ephemeris.sqlite3
- Update Dockerfile: COPY data/ephe/ instead of empty mkdir
- Update docker-compose: mount only data/cache/ volume, set EPHEMERIS_DATA_DIR
- Simplify .gitignore: ignore data/cache/ and data/ephe/*.bsp (no more 42 whitelist lines)
- Remove data/ from .dockerignore