CrossRelay stage 0+1: Go gateway with Anthropic<->Chat Completions relay, Tauri shell, bilingual management UI

- Go gateway (stdlib only): /v1/messages non-stream + SSE, /v1/messages/count_tokens,
  management API /api/* (providers CRUD, apply/restore, settings, backups, logs)
- Protocol conversion: Anthropic Messages <-> Chat Completions with a streaming
  state machine keyed by content block index (text, tool_use, parallel calls)
- ~/.claude/settings.json guarded read/write: timestamped backups, managed env
  keys only, one-click restore
- Tauri 2 shell: spawns the gateway sidecar, parses the random port from stdout,
  stdin pipe watchdog prevents orphans, kills the child on exit
- React frontend: Dashboard/Providers/Settings, zh-CN + en-US, TanStack Query
- Tests: Go table-driven + httptest integration (all green), vitest + RTL

src/components/ui/switch.tsx

@@ -0,0 +1,32 @@
+import { cn } from "@/lib/utils";
+
+export interface SwitchProps {
+  checked: boolean;
+  onCheckedChange: (checked: boolean) => void;
+  label: string;
+  id?: string;
+}
+
+export function Switch({ checked, onCheckedChange, label, id }: SwitchProps) {
+  return (
+    <button
+      id={id}
+      type="button"
+      role="switch"
+      aria-checked={checked}
+      aria-label={label}
+      onClick={() => onCheckedChange(!checked)}
+      className={cn(
+        "relative inline-flex h-5 w-9 shrink-0 items-center rounded-full transition-colors",
+        checked ? "bg-teal-700" : "bg-zinc-300",
+      )}
+    >
+      <span
+        className={cn(
+          "inline-block h-4 w-4 transform rounded-full bg-white transition-transform",
+          checked ? "translate-x-4" : "translate-x-0.5",
+        )}
+      />
+    </button>
+  );
+}