feat: add Mistral Voxtral TTS provider

[kimbotai1337]

Summary

• add a new explicit mistral TTS provider in Nerve wired through backend routes, provider config, API key management, settings UI, and command palette
• add a Mistral Voxtral service client plus tests/docs updates, with the current default Mistral voice set to Jane - Neutral for this branch
• validate the integration with targeted tests and live smoke testing against Mistral voices

Test Plan

• npx vitest --run server/lib/tts-config.test.ts server/services/mistral-tts.test.ts server/routes/api-keys.test.ts server/routes/tts.test.ts src/features/tts/useTTS.test.ts src/features/settings/AudioSettings.component.test.tsx
• npm run build
• manual smoke test in Nerve using Mistral voice playback

Notes

• the full repo test suite is currently baseline-red on unrelated existing failures outside this change set, so this PR uses targeted verification + full build
• Mistral TTS appears intermittently flaky upstream (500 Service unavailable) during testing; explicit saved voice IDs work, but provider reliability is not perfect right now

Follow-ups

• add a Mistral voice dropdown populated from /v1/audio/voices
• add retry logic / graceful handling for transient Mistral 500s

[coderabbitai]

Important

Review skipped

Draft detected.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 707a9624-2037-465d-a7a1-1fc1e57d17d8

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}