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/shared/error-boundary.tsx

@@ -1,11 +1,17 @@
 "use client";
 
+import { AlertCircle, RefreshCw } from "lucide-react";
 import { Component, type ReactNode } from "react";
 import { GlassCard } from "@/components/glass/card";
-import { AlertCircle, RefreshCw } from "lucide-react";
 
-interface Props { children: ReactNode; fallback?: ReactNode; }
-interface State { hasError: boolean; error?: Error; }
+interface Props {
+  children: ReactNode;
+  fallback?: ReactNode;
+}
+interface State {
+  hasError: boolean;
+  error?: Error;
+}
 
 export class ErrorBoundary extends Component<Props, State> {
   state: State = { hasError: false };
@@ -16,18 +22,25 @@ export class ErrorBoundary extends Component<Props, State> {
 
   render() {
     if (this.state.hasError) {
-      return this.props.fallback || (
-        <GlassCard variant="danger" className="flex flex-col items-center gap-2 py-8">
-          <AlertCircle className="size-6 text-destructive" />
-          <p className="text-sm text-text-secondary">{this.state.error?.message || "Something went wrong"}</p>
-          <button
-            type="button"
-            onClick={() => this.setState({ hasError: false })}
-            className="flex items-center gap-1 text-xs text-primary hover:text-primary/80 transition-colors"
+      return (
+        this.props.fallback || (
+          <GlassCard
+            variant="danger"
+            className="flex flex-col items-center gap-2 py-8"
           >
-            <RefreshCw className="size-3" /> Try again
-          </button>
-        </GlassCard>
+            <AlertCircle className="size-6 text-destructive" />
+            <p className="text-sm text-text-secondary">
+              {this.state.error?.message || "Something went wrong"}
+            </p>
+            <button
+              type="button"
+              onClick={() => this.setState({ hasError: false })}
+              className="flex items-center gap-1 text-xs text-primary hover:text-primary/80 transition-colors"
+            >
+              <RefreshCw className="size-3" /> Try again
+            </button>
+          </GlassCard>
+        )
       );
     }
     return this.props.children;