fix(anilist): repair SaveMediaListEntry mutation and surface update failures

The AniListUpdateEntry mutation was mangled in 54c109a when the
standardized media field block was pasted in without the media { }
wrapper: media-level fields (idMal, title, ...) sat directly on
SaveMediaListEntry (which returns MediaList), the MediaList fields
(status, startedAt, ..., user) ended up at the Mutation root, and a
stray closing brace made the document a guaranteed 400. Because the
response status was discarded, the frontend received a zeroed
AniListGetSingleAnime and blanked the anime page after every submit,
making AniList appear logged out (and the change was never saved).

- Restore the mutation to match the tested bruno request: id/mediaId/
  userId, standard media block inside media { }, MediaList fields
  inside the selection, balanced braces.
- AniListUpdateEntry and AniListDeleteEntry now return an error on
  403/non-200/unparseable responses (mirroring
  GetAniListUserWatchingList) instead of silently returning zero
  values.
- Anime.svelte guards against replacing the page data with an empty
  response and raises the API error modal instead.

Bump productVersion to 1.6.1.

wails.json

@@ -12,6 +12,6 @@
   },
   "info": {
     "productName": "AniTrack",
-    "productVersion": "1.5.5"
+    "productVersion": "1.6.1"
   }
 }