fix(core,meta,app,android,cli): number episodes the way releases do

AniList's per-season lookup searched for "<title> 2nd Season" and the
scorer picked the base entry again, so Attack on Titan seasons 2-4 and
Jigokuraku season 2 were captioned with season one's names. Episode
names came from streamingEpisodes, which is partial and numbered however
a streaming site counted. Bleach S17 and Mushishi S02/S03 had none.

AniList now walks SEQUEL relations from the match and takes each
entry's episodes from ani.zip, which carries TVDB's season, number and
absolute number. An episode row keeps all three plus its place in the
AniList entry. EpisodeGuide::get matches whichever numbering a file
uses and never answers from another season.

Episodes and fanart are stored as one enrichment. The episode list is
replaced even when empty, and the enrichment is recorded as asked, so a
film is not re-asked every run. Storing a different match drops the old
entry's episode rows. AniList's 4.75:1 bannerImage is no longer stored
as the 16:9 backdrop; ani.zip's 1920x1080 fanart is used instead.

Schema v9 adds the columns and deletes the AniList episode rows and
banners. Matches are kept. Desktop, Android and the CLI now share
service::plan and MetadataService::work. The settings text names
ani.zip. Audit and roadmap in docs/METADATA.md; bug entry B61.

docs/METADATA.md

@@ -0,0 +1,137 @@
+# Metadata
+
+How a library of filenames becomes posters, synopses and episode names, what
+was wrong with the first version of it, and where it is going. The privacy
+stance from `pstr_core::metadata` holds throughout: nothing here is requested
+until the viewer turns enrichment on, and every new source named below sits
+behind that same switch.
+
+## What a real library showed
+
+Audited against a 42-title, 758-file anime library matched on AniList
+(schema v8, October 2026). The match itself — title to AniList entry — was
+good. What hung off it was not:
+
+1. **Later seasons captioned with season one's names.** Attack on Titan
+   seasons 2–4 and Jigokuraku season 2 all stored season one's episode list.
+   The per-season lookup searched for `Attack on Titan 2nd Season`, and the
+   similarity scorer, seeing the base entry's alias inside the query, picked the
+   base entry again. That is the failure `EpisodeGuide::get` already warned
+   about: not a missing caption but a wrong one.
+2. **`streamingEpisodes` is not an episode list.** It is what a streaming site
+   published, partial and numbered however that site numbered it. Dan Da Dan
+   had 5 rows numbered 13–17, Kaiju No. 8 had 4–15, The Apothecary Diaries had
+   25–48 under two seasons at once, Bleach had 20 rows called `Untitled`, Akira
+   had a trailer. No row anywhere had a synopsis — AniList keeps none.
+3. **A release's season is not an AniList entry.** Bleach `S17` is the
+   Thousand-Year Blood War, four separate AniList entries. Mushoku Tensei `S01`
+   is two (11 + 12 episodes). Attack on Titan's season folders hold
+   absolutely-numbered files — `S2` is episodes 26–37. Mushishi's `S03` is
+   *Zoku Shou 2*, which TVDB files as the second half of season two.
+4. **Answers outlived their match.** `jujutsu kaisen 0 movie` kept the TV
+   series' 24 episode names after it was re-pinned to the film: an empty episode
+   list was never written, so the old one stayed.
+5. **Desktop art was the wrong shape.** The 16:9 tile and the library's hero
+   prefer `backdrop_url`, which on AniList is `bannerImage` — a 1900×400 strip,
+   4.75:1, cached at 640×135. Cropped to 16:9 and stretched, that is a blurred
+   sliver from the middle of a banner. Android looks right because it draws the
+   2:3 cover.
+6. **"Newest" sorts on nothing.** It reads the year from the filename, which 2
+   of 42 titles state.
+
+## Sources
+
+| Source | Key | What it is good for |
+|---|---|---|
+| **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. |
+| **TMDB** | free key | Film backdrops and logos; live-action TV. Already implemented. |
+| **TVmaze** | none | Live-action TV episodes, keyless. |
+| **AniSkip** | none | Opening and ending timestamps by MAL id and episode. |
+| **Jikan** (MAL) | none | Filler and recap flags. Timed out when tried; optional. |
+| **manami-project/anime-offline-database** | none | Every anime with its synonyms, ids and relations, as one 6 MB `.zst`. Matching against it locally sends no title anywhere. |
+| AniDB, TVDB directly | registration / paid | Covered by ani.zip, which republishes their data. |
+
+The fact the whole design turns on: **release groups number files the way TVDB
+does.** `Bleach - S17E01` is TVDB season 17; Attack on Titan's 26–96 are TVDB
+absolute numbers. ani.zip gives both for every AniList entry, so the join
+between a filename and an episode is a lookup, not a guess.
+
+## Phase 1 — correct data (done)
+
+**Seasons by relation, not by name.** `AniList::enrich` starts at the matched
+entry and follows its `SEQUEL` edges — TV formats first, a special or film only
+when it is the sole link onward (Mushishi's chain runs through an OVA). Each
+entry's episodes come from ani.zip. The walk stops as soon as every numbered file
+in the title has an answer, at the end of the chain, or after
+`MAX_CHAIN_ENTRIES`, so a one-season show costs one ani.zip request and no
+relations query at all.
+
+**One episode, three numberings.** `EpisodeMetadata` carries TVDB's
+`(season, number)`, TVDB's `absolute` number, and its `(entry_season,
+entry_number)` — the position of its entry among the franchise's TV entries,
+and its number within that entry, which is how a release that follows AniList
+rather than TVDB numbers its seasons. `EpisodeGuide::get` tries, in order:
+
+1. the season and number the file states;
+2. for a file in no season or season one, the provider's own absolute list,
+   then season one;
+3. the absolute number — but only into the season the file states, so an
+   absolutely-numbered season folder (`Attack on Titan/S2/… - 26`) finds
+   S2E1, and `S03E13` can never be answered with season one's 13th;
+4. the entry numbering, only for a season TVDB does not have at all — which is
+   what makes Mushishi `S03E01` *Zoku Shou 2* episode 1 while Mushoku Tensei
+   `S02E01`, a season TVDB does have, stays TVDB's.
+
+`streamingEpisodes` is gone.
+
+**Enrichment is recorded, empty or not.** A title's episode list and its
+fanart are one *enrichment*, stored together by `Catalog::set_enrichment` in one
+transaction that always replaces the old episode rows — so an empty answer
+clears what a previous match left behind. `title_metadata.enriched_at` records
+that it was asked, which is what keeps a film with no episodes from being
+re-asked on every match run. A new match clears it; a failed enrichment leaves it
+clear, so the title is asked again.
+
+**No banner on a 16:9 tile.** AniList's `bannerImage` is no longer stored as a
+backdrop. The backdrop is ani.zip's fanart where there is one; otherwise the tile
+letterboxes the poster.
+
+**Schema v9** adds the three numbering columns and `enriched_at`, deletes every
+stored AniList episode row and every AniList banner-as-backdrop — all of it
+`streamingEpisodes` data and wrong-shaped art — and leaves every title
+un-enriched, so the next match run (which the app starts on its own) refills
+them. Matches, hand-picked ones included, are kept.
+
+## Phase 2 — art and order
+
+- **Art slots** instead of one backdrop: poster (2:3), fanart (16:9), banner
+  (ultra-wide), logo. The hero and the 16:9 tiles take fanart; the banner only
+  ever fills an ultra-wide strip.
+- **A larger size class for the hero.** `THUMBNAIL_MAX_EDGE` is 640 for every
+  picture; the hero is drawn up to ~1600 px wide.
+- **A poster grid on desktop**, as an option or the default — AniList's covers
+  are the best art this library has, and Android already proves the layout.
+- **More of the AniList answer kept**: format, season and year, studios,
+  director, tags, popularity, status, next airing episode — all in the search
+  response already, so no extra request.
+- **Sorts**: by the displayed name (English / romaji / folder, as a setting),
+  release season, rating, popularity, recently added (needs a `first_seen`
+  column), in-progress first.
+- **Franchise grouping** from relations: the Evangelion TV series, its two films
+  and the Rebuild folder; Made in Abyss and its three films; Mushishi and its
+  specials; the Heaven's Feel trilogy. One tile each, with the parts in release
+  order on the title page.
+- **Shelves**: genre, studio, director — this library has a Satoshi Kon shelf
+  waiting in it — format, decade, airing now.
+
+## Phase 3 — reach
+
+- **Local matching** against the offline database, so only ids leave the
+  machine.
+- **Routing by title**: AniList first, then TMDB (with a key) or TVmaze for
+  whatever is not anime — Game of Thrones in a mostly-anime share.
+- **Folders of films** matched per file: four Rebuild films in one folder are
+  four entries, not one.
+- **Skip intro** from AniSkip for files without chapters, and filler flags from
+  Jikan.