feat(claude-desktop): add 3P provider switching with proxy gateway

Adds a new ClaudeDesktop AppType that writes Claude Desktop's third-party
inference profile under configLibrary/, sharing _meta.json with other
launchers (Ollama-compatible) so cc-switch can coexist with them.

Two switch modes:
- direct: provider already exposes claude-* / anthropic/claude-* model
  ids on Anthropic Messages, Claude Desktop connects to it directly.
- proxy: cc-switch's local proxy acts as the inference gateway,
  presenting only claude-* route names to Claude Desktop and mapping
  them to real upstream models. Required after Anthropic restricted
  Claude Desktop to claude-family ids.

Backend:
- New module claude_desktop_config with snapshot/rollback, official seed
  bypass, /claude-desktop/v1/{models,messages} routes, and a single
  source of truth for default proxy routes.
- Gateway token persisted in SQLite, validated on every proxied request.
- get_claude_desktop_status surfaces drift signals (stale models,
  missing routes, proxy stopped, base URL mismatch, missing token).

Frontend:
- Slim ClaudeDesktopProviderForm independent from ProviderForm,
  controlled by a top-level appId guard.
- ProviderList banner consumes the status query (5s polling) and
  renders actionable diagnostics.
- ClaudeDesktopRouteToggle in the header to start/stop the local
  gateway without touching takeover state.
- Three-locale i18n synchronised.

src/components/providers/forms/hooks/useBaseUrlState.ts

@@ -32,9 +32,9 @@ export function useBaseUrlState({
   const [geminiBaseUrl, setGeminiBaseUrl] = useState("");
   const isUpdatingRef = useRef(false);
 
-  // 从配置同步到 state（Claude）
+  // 从配置同步到 state（Claude / Claude Desktop）
   useEffect(() => {
-    if (appType !== "claude") return;
+    if (appType !== "claude" && appType !== "claude-desktop") return;
     // 只有 official 类别不显示 Base URL 输入框，其他类别都需要回填
     if (category === "official") return;
     if (isUpdatingRef.current) return;