feat(elevenlabs): register eleven_v3 in TTS model allowlist

eleven_v3 already works end-to-end (model_id passes through to the API
without validation), but was missing from ELEVENLABS_TTS_MODELS so it
never appeared in the in-product model picker or catalog metadata.

extensions/elevenlabs/speech-provider.ts

@@ -37,6 +37,7 @@ const DEFAULT_ELEVENLABS_VOICE_SETTINGS = {
 };
 
 const ELEVENLABS_TTS_MODELS = [
+  "eleven_v3",
   "eleven_multilingual_v2",
   "eleven_turbo_v2_5",
   "eleven_monolingual_v1",