feat(db): store poster, backdrop and rating on titles

§9.6 keeps rich detail out of the database except for the three fields
pure-SQL views need. Adds poster_path, backdrop_path and vote_average to
movies and series, written by the daily metadata refresh in both lanes
and filled at add time from the TMDB response the create flows already
fetch.

crates/arr-db/migrations/0022_title_artwork.sql

@@ -0,0 +1,11 @@
+-- §9.6: the three fields rich detail keeps out of the database are the ones
+-- pure-SQL views need — the in-library half of unified search (§9.2) and the
+-- library grid would otherwise cost one TMDB call per row. Nullable, no
+-- default: a title added before its first metadata refresh has no artwork
+-- yet, and TMDB itself has entries with no poster.
+ALTER TABLE movies ADD COLUMN poster_path TEXT;
+ALTER TABLE movies ADD COLUMN backdrop_path TEXT;
+ALTER TABLE movies ADD COLUMN vote_average REAL;
+ALTER TABLE series ADD COLUMN poster_path TEXT;
+ALTER TABLE series ADD COLUMN backdrop_path TEXT;
+ALTER TABLE series ADD COLUMN vote_average REAL;