feat(tts): add new OpenAI gpt-4o-mini-tts voices

Add ballad, cedar, marin, and verse to OPENAI_TTS_VOICES.
These voices were introduced with gpt-4o-mini-tts but were missing
from the validation list, causing fallback to Edge TTS.

src/tts/tts.ts

@@ -773,13 +773,17 @@ function isCustomOpenAIEndpoint(): boolean {
 export const OPENAI_TTS_VOICES = [
   "alloy",
   "ash",
+  "ballad",
+  "cedar",
   "coral",
   "echo",
   "fable",
-  "onyx",
+  "marin",
   "nova",
+  "onyx",
   "sage",
   "shimmer",
+  "verse",
 ] as const;
 
 type OpenAiTtsVoice = (typeof OPENAI_TTS_VOICES)[number];