refactor(voice): provider-agnostic backend and in-app config

Switches the voice proxy to the OpenAI audio API (/v1/audio/transcriptions and
/v1/audio/speech) so it works with OpenAI, Groq, or a local server. Adds a
Settings -> Voice tab (base URL, API key, models, voice) plus a Quick Settings
toggle, and removes the bundled Python sidecar.

Review fixes: stop mic tracks on unmount, clear the global TTS stop handler and
revoke leaked blob URLs, add fetch timeouts in the proxy, surface mic errors in
the button, trim before appending transcripts, and drop the repo-wide wav ignore.

src/components/chat/hooks/useTts.ts

@@ -1,5 +1,6 @@
 import { useCallback, useEffect, useRef, useState } from 'react';
 import { authenticatedFetch } from '../../../utils/api';
+import { voiceConfigHeaders } from '../../../hooks/useVoiceConfig';
 
 // Only one message speaks at a time across the whole app.
 let stopActive: (() => void) | null = null;
@@ -36,8 +37,14 @@ export function useTts(getText: () => string) {
     if (stopActive) stopActive = null;
   }, [reset]);
 
-  // Cleanup on unmount.
-  useEffect(() => () => reset(), [reset]);
+  // Cleanup on unmount: drop the global stop handler if it points at us, then reset.
+  useEffect(
+    () => () => {
+      if (stopActive === stop) stopActive = null;
+      reset();
+    },
+    [reset, stop],
+  );
 
   const play = useCallback(async () => {
     if (stopActive) stopActive();
@@ -63,12 +70,16 @@ export function useTts(getText: () => string) {
       const res = await authenticatedFetch('/api/voice/tts', {
         method: 'POST',
         body: JSON.stringify({ text }),
+        headers: voiceConfigHeaders(),
       });
       if (!res.ok) throw new Error(`tts ${res.status}`);
       const blob = await res.blob();
       const url = URL.createObjectURL(blob);
+      if (audioRef.current !== audio) {
+        URL.revokeObjectURL(url); // stopped while loading; don't leak the blob URL
+        return;
+      }
       urlRef.current = url;
-      if (audioRef.current !== audio) return; // stopped while loading
       audio.src = url;
       audio.load();
       await audio.play();