Fix switch toggle UI updates and subtitle selection in player settings menu

[Copilot]

The "More Options" menu had two issues: switches (高能进度条, 弹幕) didn't update UI on toggle, and the subtitle option opened a settings dialog instead of a direct selection menu like playback speed.

Changes

• Wrapped SwitchListTile in Obx: Enables reactive UI updates when GetX observable values change

// Before: UI doesn't update when value changes
SwitchListTile(
  value: plPlayerController.enableShowDanmaku.value,
  onChanged: (value) { ... },
)

// After: UI reacts to state changes
Obx(
  () => SwitchListTile(
    value: plPlayerController.enableShowDanmaku.value,
    onChanged: (value) { ... },
  ),
)

• Added showSelectSubtitle() method: Displays bottom sheet with direct subtitle selection (关闭字幕 + available subtitles), matching the pattern of showSetSpeed() and the player controls subtitle button (view.dart:660)

• Updated subtitle menu item: Now calls showSelectSubtitle() for immediate selection instead of showSetSubtitle() which opens a styling settings dialog

Original prompt

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This section details on the original issue you should resolve

<issue_title>fix</issue_title>
<issue_description>播放器更多选项的字幕选项在https://github.com/UcnacDx2/PiliPlus/pull/232会错意了

更多选项的字幕是lib/plugin/pl_player/view.dart里字幕的相同功能

他应该像播放速度那样，在菜单里实现

以及：
播放器上更多选项，预期是像lib/plugin/pl_player/view.dart上的按钮一样即点即切换，目前不是这样，修复一下
现在是：若ui状态为开，点一次实际切换为关，但ui没变动，此时若想再次操作开关均无反应
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes fix #251

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