添加登录和后端校验

完成后端设计（未在本仓库体现），通过安全的手段完成了登录鉴权

src/context/ThemeContext.tsx

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+import { createContext, useContext, useState, useCallback, useEffect } from 'react'
+import Taro, { useDidShow } from '@tarojs/taro'
+import { getTheme, setTheme as saveTheme, resolveTheme, type ThemeMode } from '../utils/store'
+import { applyPageBackground } from '../utils/themeBackground'
+
+interface ThemeContextValue {
+  theme: ThemeMode
+  resolvedTheme: 'light' | 'dark'
+  toggleTheme: () => void
+  setTheme: (t: ThemeMode) => void
+}
+
+const ThemeContext = createContext<ThemeContextValue>({
+  theme: 'auto',
+  resolvedTheme: 'light',
+  toggleTheme: () => {},
+  setTheme: () => {}
+})
+
+export { ThemeContext }
+
+type ThemeChangeListener = (result: { theme?: string }) => void
+
+type ThemeChangeApi = {
+  onThemeChange?: (listener: ThemeChangeListener) => void
+  offThemeChange?: (listener: ThemeChangeListener) => void
+}
+
+/** 主题广播事件名：自定义 tabBar 等无法继承 React Context 的独立组件通过它同步主题 */
+export const THEME_CHANGE_EVENT = 'themeChange'
+
+export function ThemeProvider({ children }: { children: React.ReactNode }) {
+  const [theme, set] = useState<ThemeMode>(getTheme())
+  const [resolvedTheme, setResolved] = useState<'light' | 'dark'>(resolveTheme(getTheme()))
+
+  const updateResolved = useCallback((mode: ThemeMode) => {
+    setResolved(resolveTheme(mode))
+  }, [])
+
+  const setTheme = useCallback((t: ThemeMode) => {
+    saveTheme(t)
+    set(t)
+    updateResolved(t)
+  }, [updateResolved])
+
+  const toggleTheme = useCallback(() => {
+    const next = resolvedTheme === 'light' ? 'dark' : 'light'
+    setTheme(next)
+  }, [resolvedTheme, setTheme])
+
+  // 广播实际生效主题，供 custom-tab-bar 等独立组件订阅
+  useEffect(() => {
+    Taro.eventCenter.trigger(THEME_CHANGE_EVENT, resolvedTheme)
+  }, [resolvedTheme])
+
+  // App 启动时立即同步页面背景（自定义导航区在 iOS 上由 backgroundColorTop 控制），
+  // 避免首屏/切换 tab 时顶部导航区先显示白色再变主题色
+  useEffect(() => {
+    applyPageBackground(resolvedTheme)
+  }, [resolvedTheme])
+
+  // 页面每次显示时（从小程序后台切回前台）重新检测系统主题
+  useDidShow(() => {
+    if (theme === 'auto') {
+      setResolved(resolveTheme('auto'))
+    }
+  })
+
+  // auto模式下监听系统主题变化
+  useEffect(() => {
+    if (theme === 'auto') {
+      // 先同步一次当前系统主题
+      setResolved(resolveTheme('auto'))
+      const listener: ThemeChangeListener = (res) => {
+        setResolved(res.theme === 'dark' ? 'dark' : 'light')
+      }
+      const themeApi = Taro as typeof Taro & ThemeChangeApi
+      themeApi.onThemeChange?.(listener)
+      return () => {
+        themeApi.offThemeChange?.(listener)
+      }
+    } else {
+      updateResolved(theme)
+    }
+  }, [theme, updateResolved])
+
+  return (
+    <ThemeContext.Provider value={{ theme, resolvedTheme, toggleTheme, setTheme }}>
+      {children}
+    </ThemeContext.Provider>
+  )
+}
+
+export function useThemeContext(): ThemeContextValue {
+  return useContext(ThemeContext)
+}