Add built-in TTS voice selector

[LooThao]

Summary

Add a voice selector UI for built-in TTS providers so users can choose provider voices directly from the TTS settings panel.

Details

• Render a voice dropdown for built-in TTS providers that define voices
• Keep custom TTS and VoxCPM voice management on their existing flows
• Use the selected provider's default voice when previewing a non-active provider
• Switch the active TTS provider when selecting a voice from a different provider tab, so the selected voice is applied consistently

Test

pnpm exec prettier components/settings/tts-settings.tsx components/settings/tts-settings-original.tsx components/settings/tts-voice-selector.tsx --check
pnpm exec eslint components/settings/tts-settings.tsx components/settings/tts-settings-original.tsx components/settings/tts-voice-selector.tsx

[chatgpt-codex-connector]

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