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/frontend/src/hooks/use-media.ts

@@ -24,9 +24,8 @@ function useMediaAction<TArgs>(fn: (args: TArgs) => Promise<MediaState>) {
 }
 
 export function useMediaQueue() {
-  return useMediaAction(
-    (input: { url: string; mode?: "music" | "screen" }) =>
-      mediaApi.queue(input.url, input.mode ?? "music"),
+  return useMediaAction((input: { url: string; mode?: "music" | "screen" }) =>
+    mediaApi.queue(input.url, input.mode ?? "music"),
   );
 }