feat(meta,core,app,android,ios): AniSkip where files have no chapters

Most files that are not fansub releases carry no chapters, so they had no
skip button. AniSkip knows where an episode's opening and ending are, by
MyAnimeList id and episode number. ani.zip sends each entry's MyAnimeList
id and enrichment now keeps it on every episode row; schema v14 adds the
column and marks AniList titles un-enriched, deleting nothing, as v13 did.

When a file has loaded with no chapter naming an opening or ending, and
its length is known, each client asks once, with enrichment on only. The
answer lives as long as the file is open. with_skip_ranges cuts it into
the chapters as chapters named Opening and Ending, so the skip button,
auto-skip, the up-next countdown and the seek bar's marks all work
through the code a chaptered file uses. A file's own opening or ending
always wins over AniSkip's.

PRIVACY.md lists what is sent: the MyAnimeList id, the episode number and
the file's length.

docs/MOBILE.md

@@ -33,6 +33,8 @@ your Drive**. See [Account and sync](ACCOUNT_AND_SYNC.md).
   the middle to pause.
 - The menu has **Episodes**, **Chapters**, **Playback speed**, the audio and subtitle tracks, and
   **Lock to landscape**.
+- **Skip opening** and **Skip ending** work as on the desktop, AniSkip included: see
+  [The player](USER_GUIDE.md#the-player).
 - Sound keeps playing with the screen off or the app in the background, with controls on the lock
   screen. Turn off **Background audio** in Settings to stop that.