#2 Season hero photo as poster bg + switch to Alpine image

**Season poster bg:** `render_season_poster()` now pulls `https://files-api.novox.be/dilbert/sports/formula1/cars/{year}.jpg`, cover-fits into 1000×1500, and overlays a vertical dark gradient so the wordmark/year/footer stay legible over any underlying photo. Falls back to the previous all-black layout if the file isn't there. **Image:** - `python:3.12-slim` → `python:3.12-alpine`. Debian was the lazy default; Alpine is the appropriate weight for this service. - `fonts-dejavu-core` → `ttf-liberation`. Same Liberation Sans Bold that Arch installs on the dev host (`/usr/share/fonts/liberation/LiberationSans-Bold.ttf`), so posters render byte-identical in dev and prod. - Drop `fastf1` from the pip install — not imported anywhere in the served code paths. Removes pandas/matplotlib/scipy tail. - Add `numpy` explicitly (was pulled in transitively by fastf1; `models/geo_json/geometry.py` imports it at module load for vector ops). **Verified locally:** - `docker build` succeeds. - Container start renders both `/posters/race/Monaco Grand Prix/2025.png` and `/posters/season/2025.png` cleanly. - Image size: 194 MB.