fix: prevent silent config fallback and data loss on startup

This commit introduces fail-fast error handling for config loading failures,
replacing the previous silent fallback to default config which could cause
data loss (e.g., all user providers disappearing).

Key changes:

Backend (Rust):
- Replace AppState::new() with AppState::try_new() to explicitly propagate errors
- Remove Default trait to prevent accidental empty state creation
- Add init_status module as global error cache (OnceLock + RwLock)
- Implement dual-channel error notification:
  1. Event emission (low-latency, may race with frontend subscription)
  2. Command-based polling (reliable, guaranteed delivery)
- Remove unconditional save on startup to prevent overwriting corrupted config

Frontend (TypeScript):
- Add event listener for "configLoadError" (fast path)
- Add bootstrap-time polling via get_init_error command (reliable path)
- Display detailed error dialog with recovery instructions
- Prompt user to exit for manual repair

Impact:
- First-time users: No change (load() returns Ok(default) when file missing)
- Corrupted config: Application shows error and exits gracefully
- Prevents accidental config overwrite during initialization

Fixes the only critical issue identified in previous code review (silent
fallback causing data loss).

src/main.tsx

@@ -9,6 +9,10 @@ import { QueryClientProvider } from "@tanstack/react-query";
 import { ThemeProvider } from "@/components/theme-provider";
 import { queryClient } from "@/lib/query";
 import { Toaster } from "@/components/ui/sonner";
+import { listen } from "@tauri-apps/api/event";
+import { invoke } from "@tauri-apps/api/core";
+import { confirm, message } from "@tauri-apps/plugin-dialog";
+import { exit } from "@tauri-apps/plugin-process";
 
 // 根据平台添加 body class，便于平台特定样式
 try {
@@ -22,15 +26,73 @@ try {
   // 忽略平台检测失败
 }
 
-ReactDOM.createRoot(document.getElementById("root")!).render(
-  <React.StrictMode>
-    <QueryClientProvider client={queryClient}>
-      <ThemeProvider defaultTheme="system" storageKey="cc-switch-theme">
-        <UpdateProvider>
-          <App />
-          <Toaster />
-        </UpdateProvider>
-      </ThemeProvider>
-    </QueryClientProvider>
-  </React.StrictMode>,
-);
+// 监听后端的配置加载错误事件：仅提醒用户并在确认后退出，不修改任何配置文件
+try {
+  void listen("configLoadError", async (evt) => {
+    const payload = evt.payload as { path?: string; error?: string } | null;
+    const path = payload?.path ?? "~/.cc-switch/config.json";
+    const detail = payload?.error ?? "Unknown error";
+
+    await message(
+      `无法读取配置文件：\n${path}\n\n错误详情：\n${detail}\n\n请手动检查 JSON 是否有效，或从同目录的备份文件（如 config.json.bak）恢复。`,
+      { title: "配置加载失败", kind: "error" },
+    );
+
+    const shouldExit = await confirm("现在退出应用以进行修复？", {
+      title: "退出确认",
+      okLabel: "退出应用",
+      cancelLabel: "取消",
+    });
+
+    if (shouldExit) {
+      await exit(1);
+    }
+  });
+} catch (e) {
+  // 忽略事件订阅异常（例如在非 Tauri 环境下）
+  console.error("订阅 configLoadError 事件失败", e);
+}
+
+async function bootstrap() {
+  // 启动早期主动查询后端初始化错误，避免事件竞态
+  try {
+    const initError = (await invoke("get_init_error")) as
+      | { path?: string; error?: string }
+      | null;
+    if (initError && (initError.path || initError.error)) {
+      const path = initError.path ?? "~/.cc-switch/config.json";
+      const detail = initError.error ?? "Unknown error";
+      await message(
+        `无法读取配置文件：\n${path}\n\n错误详情：\n${detail}\n\n请手动检查 JSON 是否有效，或从同目录的备份文件（如 config.json.bak）恢复。`,
+        { title: "配置加载失败", kind: "error" },
+      );
+      const shouldExit = await confirm("现在退出应用以进行修复？", {
+        title: "退出确认",
+        okLabel: "退出应用",
+        cancelLabel: "取消",
+      });
+      if (shouldExit) {
+        await exit(1);
+        return; // 退出流程
+      }
+    }
+  } catch (e) {
+    // 忽略拉取错误，继续渲染
+    console.error("拉取初始化错误失败", e);
+  }
+
+  ReactDOM.createRoot(document.getElementById("root")!).render(
+    <React.StrictMode>
+      <QueryClientProvider client={queryClient}>
+        <ThemeProvider defaultTheme="system" storageKey="cc-switch-theme">
+          <UpdateProvider>
+            <App />
+            <Toaster />
+          </UpdateProvider>
+        </ThemeProvider>
+      </QueryClientProvider>
+    </React.StrictMode>,
+  );
+}
+
+void bootstrap();