feat(voice): implement full voice transmit (Browser → Discord)

Frontend (useAudioTransmit.ts):
- Capture microphone via getUserMedia
- Convert Float32 to Int16 PCM at 24kHz mono
- Base64 encode and send as JSON via WebSocket
- Send voice:transmit:start/stop commands on start/stop

Backend (ws/server.ts):
- Handle voice_transmit messages from browser
- Forward PCM data to Redis channel backend:voice:transmit
- Handle voice_command messages and forward to backend:command
- discord-gateway VoiceTransmitter receives and plays to voice channel

Flow:
   Browser Mic → getUserMedia → ScriptProcessor → Int16 PCM → base64 →
   WebSocket JSON → Backend → Redis → VoiceTransmitter → Discord Voice Channel

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

services/backend/src/ws/server.ts

@@ -65,13 +65,40 @@ export function createWebSocketServer(server: Server): WebSocketServer {
     );
 
     ws.on("message", (data: Buffer) => {
-      // Binary PCM data received from browser.
-      // Since backend has no Discord client to relay to, drop it.
-      if (Buffer.isBuffer(data) && data.length > 0) {
-        logger.debug(
-          { bytes: data.length },
-          "Dropping binary PCM (no Discord client)",
-        );
+      // Handle JSON messages from browser
+      if (typeof data === 'string' || (Buffer.isBuffer(data) && data.length > 0 && data[0] === 0x7B)) {
+        try {
+          const message = JSON.parse(data.toString());
+
+          if (message.type === 'voice_transmit' && message.buffer) {
+            // Forward PCM data to Redis for discord-gateway
+            import('../shared/redis/index.js').then(({ getCommandPublisher }) => {
+              const publisher = getCommandPublisher();
+              publisher.publish('backend:voice:transmit', JSON.stringify({
+                type: 'pcm',
+                buffer: message.buffer
+              })).catch((err: Error) => {
+                logger.error({ err }, 'Failed to publish voice transmit to Redis');
+              });
+            });
+          } else if (message.type === 'voice_command' && message.command) {
+            // Forward voice commands to discord-gateway
+            import('../shared/redis/index.js').then(({ getCommandPublisher }) => {
+              const publisher = getCommandPublisher();
+              const commandId = `cmd-${Date.now()}-${Math.random().toString(36).slice(2, 9)}`;
+              publisher.publish('backend:command', JSON.stringify({
+                id: commandId,
+                type: message.command,
+                payload: {},
+                replyChannel: `reply:${commandId}`
+              })).catch((err: Error) => {
+                logger.error({ err }, 'Failed to publish voice command to Redis');
+              });
+            });
+          }
+        } catch (err) {
+          logger.debug({ err }, 'Failed to parse WebSocket message as JSON');
+        }
       }
     });