feat(subtitles): generate Jellyfin subtitles and widen halfwidth kana

- Whisper subtitle generation now works for Jellyfin playback. It reads the item's original file through toJellyfinOriginalStreamUrl and writes to a reused cache folder. For transcoded playback it uses Jellyfin's audio index
- generateJapaneseSubtitles accepts http(s) streams when an output path is set; subprocess errors redact URL tokens
- Add widenHalfwidthKana/narrowFullwidthKana and widen subtitle text at ingest (mpv sub-text, parsed cues, live primary text), so halfwidth and fullwidth duplicates merge into one cue
- Stats queries widen older stored lines, sentence search matches katakana in either width, and stats mining widens sentence/word
- Update Jellyfin, subtitle generation, and architecture docs; add changelog fragments

changes/jellyfin-subtitle-generation.md

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+type: added
+area: subtitles
+
+- Japanese subtitle generation now works while playing a Jellyfin episode. SubMiner reads the original file from the server, saves the subtitles to a cache folder, and loads them into mpv. Direct-play and transcoded playback are both supported.

changes/stats-widen-halfwidth-kana.md

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+type: fixed
+area: stats
+
+- Subtitle lines recorded before halfwidth katakana widening now show fullwidth katakana in the stats dashboard (word/kanji occurrences, sentence search), and cards mined from stats history get the fullwidth sentence and word.
+- Sentence search matches katakana in either width, so searching アンタ also finds older lines stored as ｱﾝﾀ.

changes/widen-halfwidth-kana.md

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+type: fixed
+area: overlay
+
+- Halfwidth katakana in subtitles (common in broadcast-derived Japanese subs, e.g. ｱﾝﾀ, ﾀﾞｷﾆ) now displays as normal fullwidth katakana, so lines no longer mix squashed and normal-width text. Mined sentences and stats get the fullwidth form too.