fix(voice): add HTTP API fallback for transmit commands

- Add POST /api/voice/command endpoint in backend
- Frontend transmit now sends commands via dedicated WebSocket connection
  with HTTP API fallback if WebSocket fails
- Fixes issue where transmit start command was never received by discord-gateway

Previously commands were sent via the existing dashboard WebSocket,
which may not be connected when the Transmit button is pressed.
Now each command opens a fresh WebSocket connection with HTTP fallback.

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

services/backend/src/modules/voice/voice.controller.ts

@@ -1,4 +1,5 @@
 import type { Request, Response } from "express";
+import { publishCommandNoReply } from "../../shared/redis/index.js";
 import {
   connectVoice,
   disconnectVoice,
@@ -40,3 +41,26 @@ export async function handleGetVoiceChannels(req: Request, res: Response) {
   const channels = await getVoiceChannels(guildId);
   res.json(channels);
 }
+
+export async function handleVoiceCommand(req: Request, res: Response) {
+  const command = Array.isArray(req.body.command)
+    ? req.body.command[0]
+    : req.body.command;
+
+  if (!command) {
+    return res.status(400).json({
+      error: "VALIDATION_ERROR",
+      message: "command is required",
+    });
+  }
+
+  try {
+    await publishCommandNoReply(command as string);
+    res.json({ success: true, command });
+  } catch (err) {
+    res.status(500).json({
+      error: "COMMAND_FAILED",
+      message: err instanceof Error ? err.message : "Unknown error",
+    });
+  }
+}

services/backend/src/modules/voice/voice.routes.ts

@@ -5,6 +5,7 @@ import {
   handleDisconnectVoice,
   handleGetVoiceChannels,
   handleGetVoiceStatus,
+  handleVoiceCommand,
 } from "./voice.controller.js";
 
 export function createVoiceRouter(): Router {
@@ -22,5 +23,8 @@ export function createVoiceRouter(): Router {
   // GET /api/guilds/:guildId/voice-channels
   router.get("/guilds/:guildId/voice-channels", handleGetVoiceChannels);
 
+  // POST /api/command — send arbitrary voice command (transmit start/stop)
+  router.post("/command", handleVoiceCommand);
+
   return router;
 }