Add TMDB poster picker to film detail page

- New movie_images() async function in services/tmdb.py fetches poster
  URLs from TMDB /movie/{id}/images endpoint, filtering for English
  and no-text posters only
- New GET /tmdb/posters endpoint returns list of available posters for
  a TMDB ID
- New POST /films/{film_id}/poster endpoint to save selected poster
  (mirrors the stars endpoint pattern)
- Add "Change Poster" button on detail page (only shown if film has a
  TMDB ID) that opens a 3-column grid of posters
- Selected poster gets accent border, main image updates instantly, no
  page reload needed
- Posters are cached per load to avoid refetching on re-open

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/services/tmdb.py b/services/tmdb.py
index 3618168..3574f57 100644
--- a/services/tmdb.py
+++ b/services/tmdb.py
@@ -84,6 +84,26 @@ async def movie_detail(client: httpx.AsyncClient, movie_id: int, key: str | None
     return response.json()
 
 
+async def movie_images(client: httpx.AsyncClient, movie_id: int) -> list[str]:
+    """Return list of poster URLs for a TMDB movie ID."""
+    try:
+        url = f"https://api.themoviedb.org/3/movie/{movie_id}/images"
+        response = await client.get(
+            url,
+            params={"api_key": api_key(), "include_image_language": "en,null"},
+        )
+        response.raise_for_status()
+        data = response.json()
+    except httpx.HTTPError:
+        return []
+
+    return [
+        poster_url(p["file_path"])
+        for p in data.get("posters", [])
+        if p.get("file_path")
+    ]
+
+
 def movie_payload(movie: dict, fallback: dict | None = None) -> dict:
     fallback = fallback or {}
     release_date = movie.get("release_date") or fallback.get("release_date")