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_de.arb

@@ -1737,5 +1737,58 @@
   "planReview": "{count, plural, =1{1 Karteikarte lernen} other{{count} Karteikarten lernen}}",
   "planContinue": "„{title}“ fortsetzen",
   "planNothing": "Gerade steht nichts an.",
-  "planLearningPaths": "Lernpfade"
+  "planLearningPaths": "Lernpfade",
+  "jellyfinTitle": "Jellyfin",
+  "jellyfinSubtitle": "Schau Serien und Filme von deinem eigenen Jellyfin-Server und lerne die Wörter ihrer Untertitel.",
+  "jellyfinPrivacy": "Die Adresse deines Servers und deine Anmeldung bleiben auf diesem Gerät, und die mit einem Lernset verbundenen Serien folgen dir als IDs, nie als Titel. Um die Wörter einer Zeile zu finden, fragt die App die Instanz nach ihrem Text; sie antwortet und speichert ihn nicht.",
+  "jellyfinSignedInAs": "{user} auf {server}",
+  "jellyfinSignOut": "Von Jellyfin abmelden",
+  "jellyfinAddress": "Serveradresse",
+  "jellyfinAddressHint": "jellyfin.example.org",
+  "jellyfinFind": "Weiter",
+  "jellyfinUser": "Benutzername",
+  "jellyfinPassword": "Passwort",
+  "jellyfinSignIn": "Anmelden",
+  "jellyfinQuickConnect": "Mit einem Code anmelden",
+  "jellyfinQuickConnectCode": "Gib diesen Code unter Quick Connect in einer Jellyfin-App ein, in der du angemeldet bist:",
+  "jellyfinQuickConnectWaiting": "Warte, bis der Code bestätigt ist …",
+  "jellyfinOtherServer": "Anderer Server",
+  "jellyfinUnreachable": "Unter dieser Adresse antwortet kein Server über HTTPS.",
+  "jellyfinNotEncrypted": "Diese Adresse ist nicht verschlüsselt, und dein Passwort ginge im Klartext. Nutze die HTTPS-Adresse des Servers.",
+  "jellyfinNotJellyfin": "Unter dieser Adresse ist kein Jellyfin-Server.",
+  "jellyfinWrongCredentials": "Benutzername oder Passwort stimmt nicht.",
+  "jellyfinSignedOut": "Du wurdest von Jellyfin abgemeldet. Melde dich erneut an.",
+  "jellyfinFailed": "Das hat auf dem Jellyfin-Server nicht geklappt. Versuch es noch einmal.",
+  "studysetWatch": "Von Jellyfin schauen",
+  "jellyfinBrowseTitle": "Schauen",
+  "jellyfinTied": "Mit diesem Lernset verbunden",
+  "jellyfinLibraries": "Mediatheken",
+  "jellyfinSearchHint": "Serien und Filme suchen",
+  "jellyfinTie": "Mit diesem Lernset verbinden",
+  "jellyfinUntie": "Vom Lernset lösen",
+  "jellyfinEmpty": "Hier ist nichts",
+  "jellyfinEpisode": "S{season} F{episode}",
+  "jellyfinNoPlayer": "Auf diesem Gerät können keine Videos abgespielt werden.",
+  "jellyfinNoPlayerLinux": "Auf diesem Gerät können keine Videos abgespielt werden: Dafür braucht es libmpv (das Paket libmpv2).",
+  "watchNoSubtitles": "Dieses Video hat keine Untertitel in der Sprache des Lernsets als Text, es gibt also nichts nachzuschlagen.",
+  "watchSubtitles": "Untertitel",
+  "watchTranslation": "Übersetzung",
+  "watchAudio": "Audio",
+  "watchTracks": "Audio und Untertitel",
+  "watchNone": "Keine",
+  "watchPlay": "Abspielen",
+  "watchPause": "Pause",
+  "watchPreviousLine": "Vorherige Zeile",
+  "watchNextLine": "Nächste Zeile",
+  "watchRepeatLine": "Zeile wiederholen",
+  "watchPauseAtLineEnd": "Nach jeder Zeile anhalten",
+  "watchWordsTitle": "Wörter in diesem Video",
+  "watchWordsNewOnly": "Nur neue",
+  "watchWordsFinding": "Wörter werden gesucht …",
+  "watchWordCount": "{count}×",
+  "watchAdd": "Hinzufügen",
+  "watchAdded": "{word} hinzugefügt, mit dieser Zeile",
+  "watchTapAWord": "Tipp auf ein Wort der Untertitel, um es nachzuschlagen.",
+  "watchFormOf": "Eine Form von {word}",
+  "watchFailed": "Das Video konnte nicht abgespielt werden."
 }