feat(meta,app,android,ios,cli): film backdrops and logos from TMDB by id

TVDB has no films, so ani.zip has no fanart or logo for one, and most of
the titles in a real library with nothing wide to draw were films. ani.zip
does name the TMDB entry of every AniList match. With a TMDB key stored
and AniList chosen, an entry left without a backdrop or a logo is asked
for /{movie,tv}/{id}/images: one request, by id, so no title name goes to
TMDB. A bare backdrop and a PNG logo in the viewer's language are
preferred, and a failure there only costs the art.

The TMDB key field is now offered with either provider, labelled optional
with AniList. TMDB as the provider fetches its logo the same way, and
backdrops at w1280 rather than w780. A forced run re-enriches hand-picked
titles too, so saving a key and matching everything again reaches them.

docs/USER_GUIDE.md

@@ -224,5 +224,8 @@ a video that is playing changes at once.
   **AniList** (no key needed) or **TMDB** (needs a free API key). With AniList, a title it does
   not have, such as a live-action show, is looked up on **TVmaze** next, which needs no key
   either. See [Privacy](PRIVACY.md).
+- **TMDB API key:** needed for TMDB, optional with AniList. With a key, films and shows that have
+  no wide picture or logo get TMDB's, asked for by their TMDB id alone. After saving a key,
+  **Match everything again** fetches them for titles already matched.
 - **Match the library** looks up new titles now. **Match everything again** looks up every title,
   except those you matched by hand.