Add photo cache and /media/photos endpoint

recipes.PhotoCache.CachePhoto downloads an image through the safe
Fetcher's new FetchImage (JPEG/PNG/WebP/GIF content types only, 8 MB
cap, uncached), decodes it (GIF first frame), refuses images under
300 px on the short side, scales to 1200 px and 400 px on the long side
with golang.org/x/image/draw, encodes JPEG quality 82 under
$MEALQUEST_DATA_DIR/media/photos/{id}-{size}.jpg, deduplicates by the
SHA-256 of the original bytes and records a photos row.

GET /media/photos/{id}-{400|1200}.jpg serves a stored size behind the
session with Cache-Control "private, max-age=31536000, immutable";
anything unknown is 404.

Adds golang.org/x/image v0.45.0 (approved; v0.46.0 needs Go 1.26).

Maestro task: 8a432108-d3ba-4013-ae8c-11963981d641

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

go.sum

@@ -21,6 +21,8 @@ github.com/oklog/ulid/v2 v2.1.2/go.mod h1:rcEKHmBBKfef9DhnvX7y1HZBYxjXb0cP5ExxNs
 github.com/pborman/getopt v0.0.0-20170112200414-7148bc3a4c30/go.mod h1:85jBQOZwpVEaDAr341tbn15RS4fCAsIst0qp7i8ex1o=
 github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec h1:W09IVJc94icq4NjY3clb7Lk8O1qJ8BdBEF8z0ibU0rE=
 github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec/go.mod h1:qqbHyh8v60DhA7CoWK5oRCqLrMHRGoxYCSS9EjAz6Eo=
+golang.org/x/image v0.45.0 h1:FMb1nTbH5H9vF55SriQHgFw5GnNL9Jg6L25BwXKzhB0=
+golang.org/x/image v0.45.0/go.mod h1:n62x/7RqlwXDvGsSU4u6IUTUf6KghUZ9Bt7cG/T9Fx4=
 golang.org/x/mod v0.38.0 h1:MECBjubtXD7yj4HrhIUcywNaGeNVUdfVnxmPajOk4yk=
 golang.org/x/mod v0.38.0/go.mod h1:V6Xz0pq8TQ3dGqVQ1FVHuelZpAL0uNhSkk9ogYP3c40=
 golang.org/x/oauth2 v0.36.0 h1:peZ/1z27fi9hUOFCAZaHyrpWG5lwe0RJEEEeH0ThlIs=