feat(updater): 优化更新体验与 UI

- ui: UpdateBadge 使用 Tailwind 内置过渡，支持点击打开设置，保留图标动画

- updater: 新增 UpdateContext 首启延迟检查，忽略版本键名命名空间化（含旧键迁移），并发保护

- settings: 去除版本硬编码回退；检测到更新时复用 updateHandle 下载并安装，并新增常显“更新日志”入口

- a11y: 更新徽标支持键盘触达（Enter/Space）

- refactor: 移除未使用的 runUpdateFlow 导出

- chore: 类型检查通过，整体行为与权限边界未改变

src/contexts/UpdateContext.tsx

@@ -0,0 +1,147 @@
+import React, { createContext, useContext, useState, useEffect, useCallback, useRef } from "react";
+import type { UpdateInfo, UpdateHandle } from "../lib/updater";
+import { checkForUpdate } from "../lib/updater";
+
+interface UpdateContextValue {
+  // 更新状态
+  hasUpdate: boolean;
+  updateInfo: UpdateInfo | null;
+  updateHandle: UpdateHandle | null;
+  isChecking: boolean;
+  error: string | null;
+  
+  // 提示状态
+  isDismissed: boolean;
+  dismissUpdate: () => void;
+  
+  // 操作方法
+  checkUpdate: () => Promise<void>;
+  resetDismiss: () => void;
+}
+
+const UpdateContext = createContext<UpdateContextValue | undefined>(undefined);
+
+export function UpdateProvider({ children }: { children: React.ReactNode }) {
+  const DISMISSED_VERSION_KEY = "ccswitch:update:dismissedVersion";
+  const LEGACY_DISMISSED_KEY = "dismissedUpdateVersion"; // 兼容旧键
+
+  const [hasUpdate, setHasUpdate] = useState(false);
+  const [updateInfo, setUpdateInfo] = useState<UpdateInfo | null>(null);
+  const [updateHandle, setUpdateHandle] = useState<UpdateHandle | null>(null);
+  const [isChecking, setIsChecking] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+  const [isDismissed, setIsDismissed] = useState(false);
+  
+  // 从 localStorage 读取已关闭的版本
+  useEffect(() => {
+    const current = updateInfo?.availableVersion;
+    if (!current) return;
+
+    // 读取新键；若不存在，尝试迁移旧键
+    let dismissedVersion = localStorage.getItem(DISMISSED_VERSION_KEY);
+    if (!dismissedVersion) {
+      const legacy = localStorage.getItem(LEGACY_DISMISSED_KEY);
+      if (legacy) {
+        localStorage.setItem(DISMISSED_VERSION_KEY, legacy);
+        localStorage.removeItem(LEGACY_DISMISSED_KEY);
+        dismissedVersion = legacy;
+      }
+    }
+
+    setIsDismissed(dismissedVersion === current);
+  }, [updateInfo?.availableVersion]);
+  
+  const isCheckingRef = useRef(false);
+
+  const checkUpdate = useCallback(async () => {
+    if (isCheckingRef.current) return;
+    isCheckingRef.current = true;
+    setIsChecking(true);
+    setError(null);
+
+    try {
+      const result = await checkForUpdate({ timeout: 30000 });
+
+      if (result.status === "available") {
+        setHasUpdate(true);
+        setUpdateInfo(result.info);
+        setUpdateHandle(result.update);
+
+        // 检查是否已经关闭过这个版本的提醒
+        let dismissedVersion = localStorage.getItem(DISMISSED_VERSION_KEY);
+        if (!dismissedVersion) {
+          const legacy = localStorage.getItem(LEGACY_DISMISSED_KEY);
+          if (legacy) {
+            localStorage.setItem(DISMISSED_VERSION_KEY, legacy);
+            localStorage.removeItem(LEGACY_DISMISSED_KEY);
+            dismissedVersion = legacy;
+          }
+        }
+        setIsDismissed(dismissedVersion === result.info.availableVersion);
+      } else {
+        setHasUpdate(false);
+        setUpdateInfo(null);
+        setUpdateHandle(null);
+        setIsDismissed(false);
+      }
+    } catch (err) {
+      console.error("检查更新失败:", err);
+      setError(err instanceof Error ? err.message : "检查更新失败");
+      setHasUpdate(false);
+    } finally {
+      setIsChecking(false);
+      isCheckingRef.current = false;
+    }
+  }, []);
+  
+  const dismissUpdate = useCallback(() => {
+    setIsDismissed(true);
+    if (updateInfo?.availableVersion) {
+      localStorage.setItem(DISMISSED_VERSION_KEY, updateInfo.availableVersion);
+      // 清理旧键
+      localStorage.removeItem(LEGACY_DISMISSED_KEY);
+    }
+  }, [updateInfo?.availableVersion]);
+  
+  const resetDismiss = useCallback(() => {
+    setIsDismissed(false);
+    localStorage.removeItem(DISMISSED_VERSION_KEY);
+    localStorage.removeItem(LEGACY_DISMISSED_KEY);
+  }, []);
+  
+  // 应用启动时自动检查更新
+  useEffect(() => {
+    // 延迟1秒后检查，避免影响启动体验
+    const timer = setTimeout(() => {
+      checkUpdate().catch(console.error);
+    }, 1000);
+
+    return () => clearTimeout(timer);
+  }, [checkUpdate]);
+  
+  const value: UpdateContextValue = {
+    hasUpdate,
+    updateInfo,
+    updateHandle,
+    isChecking,
+    error,
+    isDismissed,
+    dismissUpdate,
+    checkUpdate,
+    resetDismiss,
+  };
+  
+  return (
+    <UpdateContext.Provider value={value}>
+      {children}
+    </UpdateContext.Provider>
+  );
+}
+
+export function useUpdate() {
+  const context = useContext(UpdateContext);
+  if (!context) {
+    throw new Error("useUpdate must be used within UpdateProvider");
+  }
+  return context;
+}