feat(jellyfin): watch from one's own Jellyfin server and learn the words of its subtitles

Animelon's way of learning from video, from the person's own Jellyfin
server: connected per device (Settings, or a studyset's Add material ›
Watch from Jellyfin) with a name and password or a Quick Connect code,
over HTTPS only (plain HTTP only to a server on the same machine); the
token stays in the system's keyring. Shows, films and videos tied to a
studyset follow the person in their settings as the server's and the
item's ids alone (settings schema 9), named by the server when shown.

The Watch screen plays the video (video_player on Android, media_kit's
libmpv on Linux and Windows) with the line in the studyset's front
language cut into the dictionary's words with furigana, and the back
language's line beneath; a word tapped pauses the video and becomes a
card with the line and its translation as its first hint, tagged with
the show. The video's words are listed, most frequent first. The sound is
the track in the studyset's language, whichever the file marks default,
and the menu switches it; the subtitles read are a whole track, never a
forced one (which only covers what the sound doesn't say), and captions
for the hard of hearing only without plain ones. The line and its
translation take the video's width in a box of a fixed height, so the
video keeps its size; in the dark theme the video's colours glow around
it, as YouTube's ambient mode, and the words' panel takes the colour of
the episode's picture under the pointer.

A line is cut into words with one request: DictionaryEndpoint.withKeys
looks up every stretch of it that may be a word, as it stands and as
every word it may be a conjugation of, in the new dictionary_key table
(one row per key, indexed; migration dictionary-keys adds the table and
its index, nothing else), which the loader fills beside the entries.
The instance gets the text of each line looked up and keeps none of it,
as the Watch screen says.

Linux builds need libmpv-dev, and the app links libmpv: the snap stages
Ubuntu's libmpv2, makes the update-alternatives links for BLAS and LAPACK
that ffmpeg's speech recognition needs (staging never runs install
scripts), and removes what the GNOME runtime and core24 already hold, as
older copies of cairo, pango and librsvg hid the runtime's from its GTK.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_flutter/lib/l10n/app_localizations_en.dart

@@ -6423,6 +6423,185 @@ class AppLocalizationsEn extends AppLocalizations {
 
   @override
   String get planLearningPaths => 'Learning paths';
+
+  @override
+  String get jellyfinTitle => 'Jellyfin';
+
+  @override
+  String get jellyfinSubtitle =>
+      'Watch shows and films from your own Jellyfin server, and learn the words of their subtitles.';
+
+  @override
+  String get jellyfinPrivacy =>
+      'Your server\'s address and your sign-in stay on this device, and the shows tied to a studyset follow you as ids, never titles. To find the words of a line, the app asks the instance about its text, which it answers and doesn\'t keep.';
+
+  @override
+  String jellyfinSignedInAs(String user, String server) {
+    return '$user on $server';
+  }
+
+  @override
+  String get jellyfinSignOut => 'Sign out of Jellyfin';
+
+  @override
+  String get jellyfinAddress => 'Server address';
+
+  @override
+  String get jellyfinAddressHint => 'jellyfin.example.org';
+
+  @override
+  String get jellyfinFind => 'Continue';
+
+  @override
+  String get jellyfinUser => 'User name';
+
+  @override
+  String get jellyfinPassword => 'Password';
+
+  @override
+  String get jellyfinSignIn => 'Sign in';
+
+  @override
+  String get jellyfinQuickConnect => 'Sign in with a code';
+
+  @override
+  String get jellyfinQuickConnectCode =>
+      'Enter this code under Quick Connect in a Jellyfin app you\'re signed in to:';
+
+  @override
+  String get jellyfinQuickConnectWaiting =>
+      'Waiting for the code to be approved…';
+
+  @override
+  String get jellyfinOtherServer => 'Another server';
+
+  @override
+  String get jellyfinUnreachable =>
+      'No server answered at that address over HTTPS.';
+
+  @override
+  String get jellyfinNotEncrypted =>
+      'That address isn\'t encrypted, and your password would travel in the clear. Use the server\'s HTTPS address.';
+
+  @override
+  String get jellyfinNotJellyfin => 'That address isn\'t a Jellyfin server.';
+
+  @override
+  String get jellyfinWrongCredentials => 'The user name or password is wrong.';
+
+  @override
+  String get jellyfinSignedOut =>
+      'You were signed out of Jellyfin. Sign in again.';
+
+  @override
+  String get jellyfinFailed =>
+      'That didn\'t work on the Jellyfin server. Try again.';
+
+  @override
+  String get studysetWatch => 'Watch from Jellyfin';
+
+  @override
+  String get jellyfinBrowseTitle => 'Watch';
+
+  @override
+  String get jellyfinTied => 'Tied to this studyset';
+
+  @override
+  String get jellyfinLibraries => 'Libraries';
+
+  @override
+  String get jellyfinSearchHint => 'Search shows and films';
+
+  @override
+  String get jellyfinTie => 'Tie to this studyset';
+
+  @override
+  String get jellyfinUntie => 'Untie from this studyset';
+
+  @override
+  String get jellyfinEmpty => 'Nothing here';
+
+  @override
+  String jellyfinEpisode(int season, int episode) {
+    return 'S$season E$episode';
+  }
+
+  @override
+  String get jellyfinNoPlayer => 'Videos can\'t play on this device.';
+
+  @override
+  String get jellyfinNoPlayerLinux =>
+      'Videos can\'t play on this device: playing them needs libmpv (the package libmpv2).';
+
+  @override
+  String get watchNoSubtitles =>
+      'This video has no subtitles in the studyset\'s language as text, so there is nothing to look up.';
+
+  @override
+  String get watchSubtitles => 'Subtitles';
+
+  @override
+  String get watchTranslation => 'Translation';
+
+  @override
+  String get watchAudio => 'Audio';
+
+  @override
+  String get watchTracks => 'Audio and subtitles';
+
+  @override
+  String get watchNone => 'None';
+
+  @override
+  String get watchPlay => 'Play';
+
+  @override
+  String get watchPause => 'Pause';
+
+  @override
+  String get watchPreviousLine => 'Previous line';
+
+  @override
+  String get watchNextLine => 'Next line';
+
+  @override
+  String get watchRepeatLine => 'Repeat line';
+
+  @override
+  String get watchPauseAtLineEnd => 'Pause after each line';
+
+  @override
+  String get watchWordsTitle => 'Words in this video';
+
+  @override
+  String get watchWordsNewOnly => 'New only';
+
+  @override
+  String get watchWordsFinding => 'Finding the words…';
+
+  @override
+  String watchWordCount(int count) {
+    return '$count×';
+  }
+
+  @override
+  String get watchAdd => 'Add';
+
+  @override
+  String watchAdded(String word) {
+    return '$word added, with this line';
+  }
+
+  @override
+  String get watchTapAWord => 'Tap a word of the subtitles to look it up.';
+
+  @override
+  String watchFormOf(String word) {
+    return 'A form of $word';
+  }
+
+  @override
+  String get watchFailed => 'The video couldn\'t be played.';
 }
 
 /// The translations for English, as used in the United Kingdom (`en_GB`).