#3 Add session thumbs + episode-level url_poster in Kometa YAML

Closes the "empty episode tile" problem in Plex. **New endpoint:** `GET /posters/session/{ergast-name}/{year}/{slug}.png` — 1920×1080 thumb composed of the aerial of the circuit + projected track outline + GP name + bold session label with a red accent bar. **Session slugs** mirror Kometa's F1 builder episode numbering, both formats: - Standard (10 episodes): fp1, fp2, fp3, pre-qualifying, qualifying, post-qualifying, pre-race, race, post-race, highlights - Sprint (15 episodes): adds pre-sprint(-qualifying), (post-)sprint, etc. **Format detection:** `_SESSION_SPRINT` is picked when the Jolpica race entry has a `Sprint*` section; otherwise `_SESSION_STD`. **YAML feed:** `/kometa/formula-1-metadata.yml` now emits an `episodes:` block under each Plex season pointing every episode at `/posters/session/.../<slug>.png`. Kometa silently skips episodes that don't exist in the library so the same feed works for any round whatever sessions you've downloaded. **Refactor:** `_draw_track_projected` now takes `canvas_w` / `geo_center_y` so the same GeoJSON-projection logic feeds both the 2:3 race poster and the 16:9 session thumb — alignment is correct by construction in both shapes.