Add Jellyfin mappings and optimize cast queries

Performance and settings updates:

- Add a new jellyfin_library_mappings column to the settings table and wire it into the Settings model (update handling and default value). This enables storing Jellyfin library mappings in settings.
- Optimize Cast::list by loading all cast filmography in a single joined query and grouping results per cast to avoid N+1 queries.
- Remove per-item cast/staff loading in Media model to avoid repeated queries during list/search operations.
- Remove game-specific enrichment from MediaController search to stop extra game info lookups during search responses.

These changes reduce repeated DB calls and centralize Jellyfin mapping storage.

api/database.php

@@ -357,6 +357,7 @@ class Database {
                 auto_play_trailers BOOLEAN DEFAULT 0,
                 language TEXT DEFAULT 'en',
                 theme TEXT DEFAULT 'system',
+                jellyfin_library_mappings JSON,
                 created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
                 updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
             )