chore(lint): biome cleanup across services — format, sort imports, drop unused

- discord-gateway: 74 lint errors -> 0 (format, import sorting, unused
  imports/vars, dead breath var)
- backend: format + sort imports (11 warnings left: noExplicitAny)
- frontend: remove unused imports, drop dead breathing var, fix
  useExhaustiveDependencies (scroll keyed on messages), a11y biome-ignore
  for drag surface + stopPropagation container (mouse-only gestures)
- remaining warnings are false positives: index keys on static lists,
  <img> in static export (next/image unsupported), noExplicitAny

tsc --noEmit clean on all 3 services; vitest green (60+36).

services/backend/src/ws/redis-bridge.ts

@@ -1,7 +1,10 @@
-import { DISCORD_CHANNEL_TO_WS_EVENT, DISCORD_VOICE_PCM } from "../shared/index.js";
-import { createChildLogger } from "../shared/logger/index.js";
 import Redis from "ioredis";
 import { config } from "../shared/config/index.js";
+import {
+  DISCORD_CHANNEL_TO_WS_EVENT,
+  DISCORD_VOICE_PCM,
+} from "../shared/index.js";
+import { createChildLogger } from "../shared/logger/index.js";
 import { broadcastBinary, broadcastEvent } from "./broadcast.js";
 
 const logger = createChildLogger("ws.redis-bridge");

services/backend/src/ws/server.ts

@@ -1,8 +1,8 @@
 import type { Server } from "node:http";
-import { BACKEND_COMMAND, BACKEND_VOICE_TRANSMIT } from "../shared/index.js";
-import { createChildLogger } from "../shared/logger/index.js";
 import { WebSocket, WebSocketServer } from "ws";
 import { config } from "../shared/config/index.js";
+import { BACKEND_COMMAND, BACKEND_VOICE_TRANSMIT } from "../shared/index.js";
+import { createChildLogger } from "../shared/logger/index.js";
 import { setBroadcastFunctions } from "./broadcast.js";
 
 const logger = createChildLogger("ws.server");