fix(xai): keep default voice as 'ara'

Voice names are lowercase per xAI's docs, so align the default with
the existing behavior (Ara) rather than switching it to eve.

Ref: https://docs.x.ai/developers/model-capabilities/audio/voice-agent#available-voices

Author: Hormold

.changeset/xai-update-grok-voices.md

@@ -2,4 +2,4 @@
 '@livekit/agents-plugin-xai': patch
 ---
 
-update Grok realtime voices to match xAI API (eve, ara, rex, sal, leo) and change default to `eve`
+update Grok realtime voices to match xAI API (eve, ara, rex, sal, leo); default voice is now lowercase `ara`

plugins/xai/src/realtime/realtime_model.ts

@@ -8,7 +8,7 @@ type OpenAIRealtimeModelOptions = ConstructorParameters<typeof OpenAIRealtimeMod
 
 const XAI_BASE_URL = 'wss://api.x.ai/v1';
 const DEFAULT_MODEL = 'grok-4-1-fast-non-reasoning';
-const DEFAULT_VOICE = 'eve';
+const DEFAULT_VOICE = 'ara';
 
 const XAI_DEFAULT_TURN_DETECTION = {
   type: 'server_vad' as const,