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/METADATA.md

@@ -45,6 +45,7 @@ good. What hung off it was not:
 |---|---|---|
 | **AniList** GraphQL | none | Identity. Search, every alias, cover art, relations (`SEQUEL`, `PREQUEL`, `SIDE_STORY`…), studios, staff, tags, format, season, popularity, next airing episode, the MAL id. |
 | **ani.zip** `api.ani.zip/mappings?anilist_id=` | none | Everything AniList lacks, per AniList id: TVDB season, episode and absolute numbers; episode titles in several languages; TVDB synopses; 16:9 stills; air dates; runtime. Series art: TVDB **fanart at 1920×1080**, poster, banner, logo. Cross-ids for MAL, AniDB, TVDB, TMDB, Kitsu, IMDb. A community service — cache what it says. |
+| **AniSkip** `api.aniskip.com/v2/skip-times/` | none | Where an episode's opening and ending are, by MyAnimeList id and episode number, as viewers marked them. Asked at play time for files without such chapters; never stored. |
 | **TMDB** | free key | Film backdrops and logos; live-action TV. Chosen as the provider, or with AniList chosen, asked by id for art alone. |
 | **TVmaze** | none | Live-action TV: episodes with 16:9 stills and runtimes, network, status, full-HD backgrounds. No films; its "typography" art is a JPEG, so no logos. In use after AniList. |
 | **AniSkip** | none | Opening and ending timestamps by MAL id and episode. |
@@ -212,6 +213,27 @@ deleting nothing. `TitleDetails::revision` makes details written before
 `runtime` existed refetch by id on the next run; they stay on screen until the
 answer lands, rather than being blanked by the migration as schema v10 did.
 
+**AniSkip.** A file whose chapters name no opening or ending — most files
+that are not fansub releases — gets them from [AniSkip](https://aniskip.com),
+where viewers mark where an episode's opening and ending are. ani.zip sends each
+entry's MyAnimeList id with its mappings; enrichment now keeps it on every
+episode row (`episode_metadata.mal_id`), next to the episode's number within
+that entry. When such a file has loaded and its length is known, the player asks
+`api.aniskip.com/v2/skip-times/{mal_id}/{number}?types=op&types=ed&episodeLength=`
+once, with enrichment on only. The answer is kept in memory for as long as the
+file is open and never stored.
+
+`pstr_core::chapters::with_skip_ranges` cuts the answer into the file's
+chapters as chapters named `Opening` and `Ending`, so the skip button, skipping
+on its own, the up-next countdown and the marks on the seek bar all work through
+the same code as for a file that came with them. A file whose own chapters
+already name an opening or an ending keeps them: what a release says about its
+own cut beats what a viewer of another release marked.
+
+**Schema v14** adds the column and marks every AniList title un-enriched,
+deleting nothing, as v13 did. Until the next match run fills it in, AniSkip is
+not asked.
+
 ## Phase 3 — reach
 
 **Routing by title (done).** One provider for the whole library left Game of