fix(db): drop 0.8 rebuild workarounds, enforce title

With sqlx 0.9 honouring `-- no-transaction`, 0007 loses its
movie_releases_backup stash like 0014 did, and 0021 gains
the CHECK (title <> '') that #153 abandoned because the 0.8
migrator could not run a rebuild with foreign keys off. The
rebuild test now enters at migration 6 so the child links
ride through all three rebuilds, and a new test proves the
'' -> 'TBA' backfill and the rejection of new empty titles.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/arr-db/migrations/0007_movie_state_canonical.sql

@@ -1,13 +1,13 @@
+-- no-transaction
 -- #73. movies.state used missing|grabbed|imported, predating arr-core's
 -- canonical MediaState vocabulary (missing|downloading|available) that
 -- series/episodes (0005) already follow.
 --
--- SQLite can't ALTER a CHECK constraint, so this rebuilds the table -- which
--- means dropping the old copy. `movie_releases` references it with
--- ON DELETE CASCADE, so the drop would take its rows down too; stash them
--- first and restore them once the new `movies` exists with the same ids.
+-- SQLite can't ALTER a CHECK constraint, so this rebuilds the table. It runs
+-- outside a transaction (#155) so `PRAGMA foreign_keys = OFF` takes effect
+-- and dropping the old `movies` does not cascade into `movie_releases`.
 
-CREATE TABLE movie_releases_backup AS SELECT * FROM movie_releases;
+PRAGMA foreign_keys = OFF;
 
 CREATE TABLE movies_new (
     id                INTEGER PRIMARY KEY,
@@ -68,6 +68,4 @@ BEGIN
     SELECT RAISE(ABORT, 'movies require a movie root');
 END;
 
-INSERT INTO movie_releases SELECT * FROM movie_releases_backup;
-
-DROP TABLE movie_releases_backup;
+PRAGMA foreign_keys = ON;