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/discord-gateway/src/modules/command-handler/commandHandler.ts

@@ -1,3 +1,6 @@
+import type { Client } from "discord.js-selfbot-v13";
+import Redis from "ioredis";
+import { config } from "../../shared/config/config.js";
 import {
   BACKEND_COMMAND,
   type CommandMessage,
@@ -6,9 +9,6 @@ import {
   VOICE_STATUS_KEY,
 } from "../../shared/index.js";
 import { createChildLogger } from "../../shared/logger/index.js";
-import type { Client } from "discord.js-selfbot-v13";
-import Redis from "ioredis";
-import { config } from "../../shared/config/config.js";
 import type { VoiceController } from "../voice-recording/voiceController.js";
 import { GuildHandler } from "./guild.handler.js";
 import {
@@ -82,7 +82,9 @@ export class CommandHandler {
 
     // Create domain-specific handlers with their dependencies
     this.voiceHandler = new VoiceHandler(client, voiceController);
-    this.mediaHandler = new MediaHandler(client, () => voiceController.getStatus());
+    this.mediaHandler = new MediaHandler(client, () =>
+      voiceController.getStatus(),
+    );
     this.guildHandler = new GuildHandler(client);
     this.moderationHandler = new ModerationHandler(client);