feat(portal): show each season's own poster beside the season tabs (#1628)

Series detail pages now render the selected season's poster as a season
cover next to the season tabs and description, and the fullscreen episode
panel shows the same poster as a season strip above its tabs.

Resolution is TMDB-first, like the show artwork merge: the lazy season
enrichment stores `/tv/{id}/season/{n}` `poster_path` as a w342 URL in
`tmdb_season_posters` (Xtream) or `StalkerSeriesTmdbSeasonsService.posters()`
(Stalker), under the same write-only-if-changed convergence guard as the
season overview. Xtream falls back to the provider's `seasons[].cover_big`/
`cover` when it is an http(s) URL other than the show poster, because panels
repeat the show poster on every season. Stalker is TMDB-only.

The cover column is not rendered for one-season items, seasons without a
poster, or a failed image, so every fallback is today's markup. It is sized
by a new `--season-cover-width` token (96/120/144px per Settings.coverSize).
The hero poster never follows the season.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/architecture/embedded-inline-playback.md

@@ -278,6 +278,23 @@ episode" chip appears when the playing episode is outside the opened
 season. Season descriptions come from `get_series_info` seasons (Xtream)
 or `TmdbEnrichmentService.getSeason` (Stalker).
 
+The tabs and description sit in a **season card** with an optional cover
+column: the selected season's own poster (`seasonPosters` input, keyed like
+`seasonDescriptions`; TMDB season poster first, provider `seasons[].cover_big`
+next — see "Season/Episode Enrichment" in `tmdb-metadata-enrichment.md`).
+The column is sized by `--season-cover-width` (96 / 120 / 144px for
+`Settings.coverSize` small / medium / large, `apps/web/src/_cover-size.scss`;
+medium matches the About block's poster) and is not rendered at all — the
+card collapses to one column and the tabs render exactly as before — when
+the selected season has no poster, when the item has a single season (that
+poster is the show poster a few hundred pixels below the hero), or when the
+image request failed. The hero poster never follows the season: the show
+keeps its identity element, the season gets its own picture next to its own
+text. The fullscreen episode panel shows the same poster as a compact season
+strip (poster, season name, episode count) above its season tabs, under the
+same gates, from `PortalInlinePlayerComponent.seasonPosters` through
+`buildFullscreenEpisodePanelSeasons`.
+
 ### Manual watched toggle for movies
 
 Movies carry the same manual "watched" affordance as episodes, in the

docs/architecture/iptvnator-ui-guidelines.md

@@ -244,7 +244,10 @@ Movie and series covers render in three surfaces: the catalog grid
 recent card (`app-content-card`, same lib) and the dashboard rails. All of
 them size from the `--cover-grid-min-width` / `--cover-rail-width` /
 `--cover-gap` tokens that `Settings.coverSize` writes onto `<html>` as
-`data-cover-size` (`apps/web/src/_cover-size.scss`).
+`data-cover-size` (`apps/web/src/_cover-size.scss`). The same file carries
+`--season-cover-width` (96 / 120 / 144px) for the season cover beside the
+season tabs on series detail pages; medium equals the About block's 120px
+poster so browse and watch share one secondary-poster size.
 
 ### Posters-only wall
 

docs/architecture/tmdb-metadata-enrichment.md

@@ -248,6 +248,25 @@ routinely fill it with a bare cover-image URL —
 `sanitizeProviderOverview` (`@iptvnator/shared/interfaces`) treats a
 URL-only value as absent, and the stored TMDB overview fills the gap.
 
+The same payload's `poster_path` — every TMDB season has its own poster,
+distinct from the show poster on most shows — is stored as a full `w342`
+URL (`tmdbSeasonPosterUrl`) in `tmdb_season_posters[seasonKey]` beside the
+overview, under the same write-only-if-changed convergence guard. Stalker
+keeps it in `StalkerSeriesTmdbSeasonsService.posters(tmdbId)` next to
+`descriptions(tmdbId)`, dropped together with the entry when a replacement
+fetch fails. Season posters resolve **TMDB-first**, like the show artwork
+merge (`prefer(tmdbPoster, provider)`): `buildSeasonPosters`
+(`libs/portal/xtream/feature/src/lib/serial-details/season-posters.util.ts`)
+takes the stored TMDB poster and falls back to the provider's
+`seasons[].cover_big`/`cover` from `get_series_info`, accepted only as a
+trimmed http(s) URL that differs from the show poster because panels repeat
+it on every season. Stalker has no provider season art, so it is TMDB-only.
+The detail views render the selected season's poster as the season cover
+beside the season tabs and in the fullscreen episode panel's season strip;
+both are withheld for one-season items (that poster is the show poster) and
+fold on a failed image request. Contract: "Two-State Detail Layout" in
+`embedded-inline-playback.md`.
+
 The season number `{n}` is the provider's episode season number, with one
 correction (`resolveEnrichmentSeasonNumber` in
 `libs/shared/interfaces/src/lib/season-marker.util.ts`): providers often