QVAC-20550 feat[api]: separate TTS language validation per engine

[ishanvohra2]

🎯 What problem does this PR solve?

• Chatterbox and Supertonic support different language sets, but the SDK validated both against one shared 4-language enum (en, es, de, it).
• Chatterbox actually supports 18 multilingual languages — most were rejected by the schema.
• Supertonic accepted de/it, which it never supports at runtime (native engine only handles en/es/fr/pt/ko).

📝 How does it solve it?

• Split the single language enum into engine-specific lists: TTS_CHATTERBOX_LANGUAGES (18) and TTS_SUPERTONIC_LANGUAGES (5).
• Wire each into its own runtime config schema (ttsChatterboxRuntimeConfigSchema / ttsSupertonicRuntimeConfigSchema).
• Kept TTS_LANGUAGES for backwards compatibility (now the union, which equals the chatterbox 18 since supertonic is a subset).
• Added TtsChatterboxLanguage / TtsSupertonicLanguage types.

🧪 How was it tested?

• Added/updated unit tests in tts-schemas.test.ts: asserts all 18 chatterbox languages parse, the supertonic subset parses, supertonic rejects chatterbox-only languages (de), and a chatterbox load config accepts tr.
• bun run test/unit/tts-schemas.test.ts → 18/18 tests, 67/67 asserts pass.

🔌 API Changes

import {
  TTS_CHATTERBOX_LANGUAGES, // en, es, fr, de, it, pt, nl, pl, tr, sv, da, fi, no, el, ms, sw, ar, ko
  TTS_SUPERTONIC_LANGUAGES, // en, es, fr, pt, ko
  type TtsChatterboxLanguage,
  type TtsSupertonicLanguage,
} from "@qvac/sdk";

// Chatterbox now accepts all 18 multilingual languages
await loadModel({
  modelSrc: ...,
  modelConfig: { ttsEngine: "chatterbox", language: "tr" },
});

Note: Supertonic's accepted language set is now correctly restricted to en/es/fr/pt/ko. de/it are no longer accepted for Supertonic configs — they never produced valid audio (the native engine only supports the 5-language subset), so this corrects previously-broken validation rather than removing working functionality.

---

• To see the specific tasks where the Asana app for GitHub is being used, see below:
  • https://app.asana.com/0/0/1215594274579707

[ishanvohra2]

/review

[github-actions]

Tier-based Approval Status

**PR Tier:** TIER1

**Current Status:** ✅ APPROVED

**Requirements:**
- 1 Team Member approval ✅ (1/1)
- 1 Team Lead OR Management approval ✅ (1/1)



---
*This comment is automatically updated when reviews change.*