Add build.sh for Cloudflare Pages env-based config injection

- Add build.sh that generates auth-config.js from environment variables
  (API_BASE_URL, GOOGLE_CLIENT_ID, ALLOWED_EMAILS) at build time
- Move email whitelist from hardcoded login.html to window.ALLOWED_EMAILS
  in auth-config.js, so it can be configured via env vars
- Reset auth-config.js to placeholder defaults in repo
- Update README.md and README_CN.md deployment docs for both options

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/auth-config.js

@@ -1,28 +1,14 @@
-window.API_CONFIG = { baseUrl: 'https://api-view.cathiefish.org' };
-
-/**
- * Google OAuth Configuration
- * Configure your Google OAuth Client ID here
- * Access control is managed via the test users list in GCP Console
- */
+window.API_CONFIG = { baseUrl: 'https://xxx.xxx.com' };
 
 const AUTH_CONFIG = {
-    // Client ID obtained from GCP Console
-    // Replace with your actual Client ID
-    clientId: '136939086552-bt28icv34nucmjna8hfndr6bopr5qcp4.apps.googleusercontent.com',
-
-    // Authentication success callback
+    clientId: 'xxxxxxxxxxxxxxxxxxxxxxxxxx.apps.googleusercontent.com',
     onSuccess: (user) => {
         console.log('Authentication successful:', user.email);
-        // Additional logic can be added here, e.g. logging
     },
-
-    // Authentication failure callback
     onError: (error) => {
         console.error('Authentication error:', error);
-        // Error handling logic can be added here
     }
 };
 
-// Export configuration
 window.AUTH_CONFIG = AUTH_CONFIG;
+window.ALLOWED_EMAILS = ['your-email@gmail.com'];