Series drill-down: mark downloading episodes and seasons

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

SPECS.md

@@ -70,7 +70,7 @@ Notes:
 - **Calendar view (F5):** a two-week window (starting today, moved a week at a time with `[`/`]`, `t` returns to today) with the library's movie releases and airing episodes, grouped by day. Radarr `GET /calendar` supplies the cinema, digital and physical release dates (taken as written: midnight UTC means that calendar day) and Sonarr `GET /calendar?includeSeries=true` the episodes with their air time (shown in local time). Unmonitored items are included with `u`. A movie appears once per release date in the window. Each entry shows type, title, episode or release kind and status (downloaded / missing / upcoming); the detail pane shows poster and plot; `Enter`/`i` starts the release search and `s` an automatic search.
 - **Download notifications:** a background poller (independent of the visible view) reads SABnzbd's history every 15 s and announces downloads that reach `Completed` or `Failed` as a popup and log entry; the first poll only records the current state. `ui.notify_downloads` (default true) and `ui.bell` (default false, rings the terminal bell) control it. Connection errors are not reported here, the indicators and the log already do that.
 - **Trakt lists:** while the search box of Movies or Series is empty, the list shows one of Trakt's public lists instead of search results: trending now (`/movies|shows/trending`, "N watching"), most watched this week (`/…/watched/weekly`, "N watched it"), anticipated (`/…/anticipated`, "on N lists"), popular (`/…/popular`), and for movies the US box office of last weekend (`/movies/boxoffice`, "$N last weekend"); 20 titles each (`page=1&limit=20`), with the headers `trakt-api-key` (the client ID, `trakt.client_id` or `ARR_TUI_TRAKT_CLIENT_ID`), `trakt-api-version: 2`, `Content-Type` and `User-Agent`. Every entry is looked up in Radarr (`tmdb:<id>`) or Sonarr (`tvdb:<id>`), at most four at a time, so it behaves like a search result (details, poster, tick when in the library, add, releases); entries without that id or unknown to the service are left out, in list order otherwise. `[` `]` switch lists (also from the empty search box), `r` reloads; a fetched list is shown again for 15 minutes without asking. Without a client ID the list says how to get one. Changing the client ID or a service in the Config view drops the fetched lists. `ARR_TUI_TRAKT_URL` points the client at another server (used by `dev/screenshots`).
-- **Downloading in the Library:** while the Library is visible it reads the Radarr and Sonarr queues (`/queue`, matched to titles by `movieId` / `seriesId`) when it opens, every 10 s, and 3 s after a grab. A title with queue entries gets a blue mark (filled when monitored, hollow when not) instead of the green or grey one, and its details a line "Downloading 45% · 0:06:12 left" (series: "Downloading N episodes"). A queue that cannot be read leaves the marks as they were. After a successful grab the release list closes (if nothing was opened on top of it).
+- **Downloading in the Library:** while the Library is visible it reads the Radarr and Sonarr queues (`/queue`, matched to titles by `movieId` / `seriesId`) when it opens, every 10 s, and 3 s after a grab. A title with queue entries gets a blue mark (filled when monitored, hollow when not) instead of the green or grey one, and its details a line "Downloading 45% · 0:06:12 left" (series: "Downloading N episodes"). A queue that cannot be read leaves the marks as they were. A series' seasons and episodes (the drill-down) read the Sonarr queue in the same way while open (when it opens and every 10 s, matched by `seriesId` and `episodeId`): an episode in the queue gets the blue mark, "downloading 45%" as its status (unless it already has a file, i.e. an upgrade) and the "Downloading" line in its details; a season with such episodes gets the blue mark and "Downloading N episode(s)". When an episode leaves the queue the episodes are loaded again, so its status follows. After a successful grab the release list closes (if nothing was opened on top of it).
 - **Disk cache:** posters and casts are kept between runs in `os.UserCacheDir()/arr-tui` (`$XDG_CACHE_HOME` or `~/.cache` on Linux, `~/Library/Caches` on macOS; directories `0700`, files written atomically). Posters are stored as decoded (at most 640 or 160 pixels tall, JPEG quality 90), one file per poster and size (small copy for block characters, large for real images) under `posters-v2/<hash>.img` (the folder is versioned: folders of earlier storage formats are deleted at startup, so their files are not used as they are); a file is used for 30 days (by its modification time) and dropped when it cannot be decoded; at startup files older than that are deleted, then the oldest until the rest fit 200 MB. Casts are one `people.json` (key = `movie:tmdb:<id>` / `show:tvdb:<id>`, with the time it was fetched); entries are used for 7 days, at most 2000 are kept (the oldest go first), titles Trakt does not know are kept as having no cast; new casts are written 5 s after the last one and when the program quits. Changing the Trakt client ID keeps the casts and only forgets failed lookups. Trakt list titles: whether a title is in the library is asked every time (`GET movie?tmdbId=` / `series?tvdbId=`, a quick query of the server's own database; the answer is checked against the id, as a version that ignores the filter sends the whole library); for titles that are not, the Radarr/Sonarr lookup (which asks the metadata provider, about a second each) is kept in `lookups.json` (key = `tmdb:<id>` / `tvdb:<id>`, the result as the server sent it, with the time it was fetched) for 3 days, at most 2000, written like the casts. The Trakt list itself is fetched again after 15 minutes as before.
 - **Season posters:** the series drill-down reads the series with `includeSeasonImages=true` (Sonarr only sends season posters when asked, and keeps no copy of them: they are TheTVDB links, fetched without credentials). A selected season or episode shows its season's poster; seasons without one, or whose poster cannot be loaded, show the series poster.
 - **Cast:** with a Trakt client ID, every details pane (search results, Trakt lists, Library, Calendar, the series drill-down) shows the director(s) of a movie or the "created by" credits of a series and up to 8 cast members with their characters below the plot ("and N more" after that). The title is found on Trakt by its TMDb id (movies) or TVDB id (series), else IMDb id (`/search/<type>/<id>?type=movie|show`), then `/movies|shows/<trakt id>/people` is read. Casts are cached, also on disk (see Disk cache; failures are retried after two minutes) and, like posters, only loaded once the selection has rested for 120 ms, so a held arrow key does not spend Trakt's allowance (500 requests per five minutes).