feat(dl): add --animeapi and --enrich options for anime metadata and tagging

Add AnimeAPI integration to resolve anime database IDs (MAL, AniList, Kitsu, etc.) to TMDB/IMDB/TVDB for MKV tagging. The --enrich flag overrides show title and fills in year when missing from the service.

- Add animeapi-py dependency for cross-platform anime ID resolution
- Add --animeapi option (e.g. mal:12345, anilist:98765, defaults to MAL)
- Add --enrich flag to override title/year from external sources
- Remove --tmdb-name and --tmdb-year in favor of unified --enrich
- Update REST API params and docs to match

unshackle/core/api/routes.py

@@ -623,12 +623,12 @@ async def download(request: web.Request) -> web.Response:
               tmdb_id:
                 type: integer
                 description: Use this TMDB ID for tagging (default - None)
-              tmdb_name:
+              animeapi_id:
+                type: string
+                description: Anime database ID via AnimeAPI, e.g. mal:12345 (default - None)
+              enrich:
                 type: boolean
-                description: Rename titles using TMDB name (default - false)
-              tmdb_year:
-                type: boolean
-                description: Use release year from TMDB (default - false)
+                description: Override show title and year from external source (default - false)
               no_folder:
                 type: boolean
                 description: Disable folder creation for TV shows (default - false)