feat(subtitles): add regex subtitle filters with built-in presets (#318)

- Add `subtitleFilter` config with four presets: parentheses, brackets, speaker prefix and music symbols. Custom regex rules run after the presets.
- Filter primary text where it enters the app (live `sub-text` and parsed cues), so the overlay, sidebar, mining and stats all get the same filtered text.
- Changes hot-reload: the current line is read again and the active track is parsed again, using the filter config as the prefetch parse key.
- Add a custom rule editor in Settings under Behavior → Subtitle Filters that checks patterns as you type.
- Update the config example, the configuration docs and the architecture domains doc, and add a changelog fragment.

docs-site/configuration.md

@@ -52,7 +52,7 @@ SubMiner watches the config file while running. When it changes, live settings a
 
 These apply live:
 
-- `subtitleStyle`, `subtitleSidebar`, `subtitleSelection`, `keybindings`, `shortcuts`
+- `subtitleStyle`, `subtitleSidebar`, `subtitleSelection`, `subtitleFilter`, `keybindings`, `shortcuts`
 - `logging.level`, `logging.rotation`, `logging.files`
 - `secondarySub.defaultMode`, `youtube.primarySubLanguages`, `youtube.subtitleSource`
 - `mpv.aniskipEnabled`, `mpv.aniskipButtonKey`, `stats.toggleKey`, `stats.markWatchedKey`
@@ -221,6 +221,29 @@ Sidebar custom properties: `--subtitle-sidebar-max-width` (`420px`), `--subtitle
 
 If `embedded` layout places the video oddly on your system, switch back to `overlay`.
 
+### Subtitle filters {#subtitle-filters}
+
+Removes unwanted text from primary subtitles, such as speaker names, readings and sound descriptions. Filtering happens as the line arrives, so the overlay, sidebar, mined sentences and stats all see the filtered text. A line left with no words is hidden. In the settings window, find it under **Behavior → Subtitle Filters**.
+
+| Key                                    | Default | What it does                                                                                                 |
+| -------------------------------------- | ------- | ------------------------------------------------------------------------------------------------------------ |
+| `subtitleFilter.presets.parentheses`   | `false` | Remove `（…）` and `(…)` anywhere in a line. A line wrapped entirely in parentheses (inner thoughts) is kept |
+| `subtitleFilter.presets.brackets`      | `false` | Remove `［…］`, `[…]`, `【…】` and `〔…〕`, such as sound effects                                            |
+| `subtitleFilter.presets.speakerPrefix` | `false` | Remove a short name before a colon at the start of a line, as in `山田：`                                    |
+| `subtitleFilter.presets.musicSymbols`  | `false` | Remove `♪`, `♫` and `♬`                                                                                      |
+| `subtitleFilter.customRules`           | `[]`    | Your own regex rules, applied in order after the presets                                                     |
+
+Each custom rule is `{ "name", "pattern", "replacement", "enabled" }`. Patterns are JavaScript regular expressions compiled with the `gmu` flags, so `^` and `$` match each line. An empty `replacement` removes the match.
+
+```jsonc
+{
+  "subtitleFilter": {
+    "presets": { "parentheses": true },
+    "customRules": [{ "name": "Join lines", "pattern": "\\n", "replacement": "", "enabled": true }],
+  },
+}
+```
+
 ### Subtitle position
 
 You can also drag subtitles with `Right-click + drag` while watching.