feat(settings): add app visibility settings

Allow users to choose which apps (Claude, Codex, Gemini, OpenCode) to display on the homepage.

- Add VisibleApps type and settings field in both frontend and backend
- Refactor AppSwitcher to render apps dynamically based on visibility
- Extract ToggleRow component for reuse
- Add i18n support for app visibility settings

src/components/ui/toggle-row.tsx

@@ -0,0 +1,41 @@
+import { Switch } from "@/components/ui/switch";
+
+export interface ToggleRowProps {
+  icon: React.ReactNode;
+  title: string;
+  description?: string;
+  checked: boolean;
+  onCheckedChange: (value: boolean) => void;
+  disabled?: boolean;
+}
+
+export function ToggleRow({
+  icon,
+  title,
+  description,
+  checked,
+  onCheckedChange,
+  disabled,
+}: ToggleRowProps) {
+  return (
+    <div className="flex items-center justify-between gap-4 rounded-xl border border-border bg-card/50 p-4 transition-colors hover:bg-muted/50">
+      <div className="flex items-center gap-3">
+        <div className="flex h-8 w-8 items-center justify-center rounded-lg bg-background ring-1 ring-border">
+          {icon}
+        </div>
+        <div className="space-y-1">
+          <p className="text-sm font-medium leading-none">{title}</p>
+          {description ? (
+            <p className="text-xs text-muted-foreground">{description}</p>
+          ) : null}
+        </div>
+      </div>
+      <Switch
+        checked={checked}
+        onCheckedChange={onCheckedChange}
+        disabled={disabled}
+        aria-label={title}
+      />
+    </div>
+  );
+}