perf(voice): reduce transmit latency

- FFmpeg: frame_duration 10ms, compression_level 0, nobuffer/low_delay flags, minimal probe
- Frontend: buffer 4096→1024 samples (~170ms→~42ms), faster base64 with chunking
- Remove processor.connect(destination) to avoid audio feedback loop

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/frontend/src/shared/hooks/useAudioTransmit.ts

@@ -58,10 +58,10 @@ export function useAudioTransmit(socketRef: {
     const audioContext = new AudioContextCtor({ sampleRate: SAMPLE_RATE });
     audioContextRef.current = audioContext;
     const source = audioContext.createMediaStreamSource(stream);
-    const processor = audioContext.createScriptProcessor(4096, 1, 1);
+    const processor = audioContext.createScriptProcessor(1024, 1, 1);
     processorRef.current = processor;
     source.connect(processor);
-    processor.connect(audioContext.destination);
+    // Don't connect processor to destination (no monitoring feedback)
     processor.onaudioprocess = (event) => {
       if (!socketRef.current || socketRef.current.readyState !== WebSocket.OPEN)
         return;
@@ -70,15 +70,15 @@ export function useAudioTransmit(socketRef: {
       for (let i = 0; i < inputData.length; i++)
         pcmData[i] = Math.max(-1, Math.min(1, inputData[i])) * 32767;
 
-      // Convert to base64
-      const bytes = new Uint8Array(pcmData.buffer);
-      let binary = '';
-      for (let i = 0; i < bytes.length; i++) {
-        binary += String.fromCharCode(bytes[i]);
+      // Fast base64 using Uint8Array + btoa
+      const uint8 = new Uint8Array(pcmData.buffer);
+      let base64 = '';
+      const chunkSize = 8192;
+      for (let i = 0; i < uint8.length; i += chunkSize) {
+        const chunk = uint8.subarray(i, i + chunkSize);
+        base64 += btoa(String.fromCharCode(...chunk));
       }
-      const base64 = btoa(binary);
 
-      // Send as JSON for backend to forward to Redis
       socketRef.current.send(JSON.stringify({
         type: 'voice_transmit',
         buffer: base64