feat: add UpdateMediaItemChapterMetadata query

- Add SQL query to update chapter metadata in media_items table
- Enables caching of detected chapter structures

internal/database/queries/queries.sql

@@ -1939,6 +1939,12 @@ DO UPDATE SET
     updated_at = NOW()
 RETURNING *;
 
+-- name: UpdateMediaItemChapterMetadata :one
+UPDATE media_items
+SET chapter_metadata = $2, updated_at = NOW()
+WHERE id = $1
+RETURNING *;
+
 -- name: GetReadingSpeed :one
 SELECT * FROM reading_speed
 WHERE user_id = $1 AND media_item_id = $2;