feat(离线): 界面离线可看 —— GET 响应本地缓存 + 同步凭证持久化 (离线不清库) + 左上角离线徽标 (与 Windows 外壳分支同源)

src/auth/AuthContext.jsx

@@ -1,5 +1,5 @@
 import { createContext, useContext, useEffect, useState } from 'react'
-import { api, getToken, setToken, setRememberFlag, setCurrentUserId } from '../api/client.js'
+import { api, getToken, setToken, setRememberFlag, setCurrentUserId, clearApiCache } from '../api/client.js'
 import { disconnectAndClearPowersync } from '../lib/powersync/db.js'
 
 const AuthContext = createContext(null)
@@ -51,6 +51,8 @@ export function AuthProvider({ children }) {
     setRememberFlag(false)
     setUser(null)
     setCurrentUserId('')
+    try { clearApiCache() } catch { /* ignore */ }
+    try { localStorage.removeItem('iboard_ps_cred') } catch { /* ignore */ }
     // 断开同步并清空本地 SQLite (0.2.1 离线编辑)
     try { await disconnectAndClearPowersync() } catch { /* ignore */ }
   }