feat(tts): add TTS buttons to PlanView and FilesView markdown preview with configurable input mode (#1443)

Add TTS controls to markdown preview surfaces so users can listen to plans
and markdown files directly from the preview toolbar.

Changes:
- Add read-aloud / stop buttons to PlanView markdown preview.
- Add read-aloud / stop buttons to FilesView markdown preview for markdown files.
- Respect the existing showMessageTTSButtons preference in both preview views.
- Add a persisted ttsInputMode setting with sanitized/raw modes.
- Keep sanitized mode as the default for backward compatibility.
- Allow raw markdown only for server TTS providers that can handle markdown.
- Always use sanitized text for browser and macOS say fallback paths.
- Add Voice Settings controls for TTS input mode.
- Add i18n keys for the new preview buttons and setting labels.
- Merge latest main and preserve newer FilesView toolbar/editor changes.

Validation:
- bun test packages/ui/src/stores/useConfigStore.test.ts packages/ui/src/components/chat/message/parts/ToolPart.test.ts packages/web/server/lib/tts/routes.test.js
- bun run type-check
- bun run lint
- git diff --check

---------

Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>

packages/ui/src/lib/i18n/messages/ko.ts

@@ -1741,6 +1741,10 @@ export const dict: Record<I18nKey, string> = {
   'chat.messageBody.tts.stopSpeaking': '읽기 중지',
   'chat.messageBody.tts.readAloud': '소리 내어 읽기',
   'chat.messageBody.tts.readAloudWithProvider': '소리 내어 읽기({provider} 음성)',
+  'planView.tts.readAloud': '계획 소리 내어 읽기',
+  'planView.tts.stopSpeaking': '읽기 중지',
+  'filesView.tts.readAloud': '파일 소리 내어 읽기',
+  'filesView.tts.stopSpeaking': '읽기 중지',
   'chat.messageBody.toast.noProject': '이 세션의 프로젝트를 찾을 수 없음',
   'chat.messageBody.toast.savePlanFailed': '플랜 저장 실패',
   'chat.messageBody.toast.planSaved': '플랜이 저장되었습니다',