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/components/voice/mic-control.tsx

@@ -1,8 +1,8 @@
 "use client";
 
+import { Mic, MicOff } from "lucide-react";
 import { GlassCard } from "@/components/glass/card";
 import { Button } from "@/components/ui/button";
-import { Mic, MicOff } from "lucide-react";
 
 interface MicControlProps {
   connected: boolean;
@@ -29,11 +29,17 @@ export function MicControl({
           disabled={!connected}
           className="h-9"
         >
-          {active ? <Mic className="size-4 mr-1" /> : <MicOff className="size-4 mr-1" />}
+          {active ? (
+            <Mic className="size-4 mr-1" />
+          ) : (
+            <MicOff className="size-4 mr-1" />
+          )}
           {active ? "Live" : "Muted"}
         </Button>
         <div className="flex-1 flex items-center gap-2">
-          <span className="text-[10px] text-text-secondary/60 font-mono">Vol</span>
+          <span className="text-[10px] text-text-secondary/60 font-mono">
+            Vol
+          </span>
           <input
             type="range"
             min={0}
@@ -42,7 +48,9 @@ export function MicControl({
             onChange={(e) => onVolumeChange(Number(e.target.value))}
             className="flex-1 h-1 appearance-none bg-glass-border rounded-full accent-primary [&::-webkit-slider-thumb]:appearance-none [&::-webkit-slider-thumb]:size-3 [&::-webkit-slider-thumb]:rounded-full [&::-webkit-slider-thumb]:bg-primary [&::-webkit-slider-thumb]:shadow-[0_0_8px] [&::-webkit-slider-thumb]:shadow-primary/60"
           />
-          <span className="text-[10px] font-mono text-text-secondary w-8 text-right">{volume}%</span>
+          <span className="text-[10px] font-mono text-text-secondary w-8 text-right">
+            {volume}%
+          </span>
         </div>
       </div>
     </GlassCard>