feat(overlay): add subtitle selection modal and Jellyfin 12 fixes

- Add an optional subtitle selection modal for primary/secondary mpv tracks (subtitleSelection.enabled, g-s sequence shortcut) with key-sequence conflict handling
- Authenticate Jellyfin URLs with the ApiKey query, answer remote keep-alives, clear now-playing on stop, and restore episode titles in Anki misc info
- Honor the configured mpv executable when Jellyfin starts playback via a shared mpv-process launcher
- Bump electron-builder to 26.16.1
- Condense and reconcile changelog fragments; update config example and docs

docs-site/shortcuts.md

@@ -88,6 +88,7 @@ Mouse-hover playback behavior is configured separately from shortcuts: `subtitle
 | `Ctrl+Shift+T`     | Open TsukiHime subtitle search modal (EN/JA tabs)       | `shortcuts.openTsukihime`                 |
 | `Ctrl/Cmd+N`       | Toggle overlay notification history panel                | `shortcuts.toggleNotificationHistory`      |
 | `Ctrl+Alt+C`       | Open the manual YouTube subtitle picker                  | `keybindings`                              |
+| `g` then `s`       | Select primary and secondary subtitles, when enabled     | `shortcuts.openSubtitleSelection`                                                               |
 | `Ctrl+Alt+S`       | Open subtitle sync (subsync) modal                       | `shortcuts.triggerSubsync`                 |
 | `Ctrl/Cmd+A`       | Append clipboard video path to mpv playlist              | `shortcuts.appendClipboardVideoToQueue`    |
 | `\`                | Toggle subtitle sidebar                                  | `subtitleSidebar.toggleKey` (overlay) / `shortcuts.toggleSubtitleSidebar` (mpv session binding) |
@@ -98,6 +99,8 @@ Mouse-hover playback behavior is configured separately from shortcuts: `subtitle
 
 The stats toggle is handled inside the focused visible overlay window. It is configurable through the top-level `stats.toggleKey` setting and defaults to `Backquote`.
 
+Enable the subtitle selector in **Settings → Behavior → Subtitle Selection**. Its shortcut overrides mpv subtitle selection only while enabled. In the focused overlay, press the second key within one second. Single-key bindings take priority: if `g` already has an action in SubMiner or mpv, `g-s` is disabled with a conflict warning, and `g` still runs immediately. Remap the sequence or remove the conflicting single-key binding. The existing `y` prefix is reserved for its built-in commands. mpv bindings are checked on connection, configuration changes, and overlay focus; refresh the overlay after changing another script's bindings. See [subtitle selection](/configuration#subtitle-selection).
+
 The subtitle sidebar toggle is overlay-local and only opens when SubMiner has a parsed cue list for the active subtitle source.
 
 In the sidebar, `Enter` seeks the keyboard-focused cue. `Space` keeps its configured playback action, normally pause/resume, even when a cue has focus.