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>

build.sh

@@ -0,0 +1,31 @@
+#!/bin/sh
+# Build script for Cloudflare Pages
+# Generates auth-config.js from environment variables
+#
+# Set these in Cloudflare Pages > Settings > Environment Variables:
+#   API_BASE_URL       - Backend API URL (e.g. https://api.yourdomain.com)
+#   GOOGLE_CLIENT_ID   - Google OAuth Client ID
+#   ALLOWED_EMAILS     - Comma-separated email whitelist (e.g. alice@gmail.com,bob@gmail.com)
+
+API_BASE_URL="${API_BASE_URL:-https://xxx.xxx.com}"
+GOOGLE_CLIENT_ID="${GOOGLE_CLIENT_ID:-xxxxxxxxxxxxxxxxxxxxxxxxxx.apps.googleusercontent.com}"
+ALLOWED_EMAILS="${ALLOWED_EMAILS:-your-email@gmail.com}"
+
+cat > frontend/auth-config.js << JSEOF
+window.API_CONFIG = { baseUrl: '${API_BASE_URL}' };
+
+const AUTH_CONFIG = {
+    clientId: '${GOOGLE_CLIENT_ID}',
+    onSuccess: (user) => {
+        console.log('Authentication successful:', user.email);
+    },
+    onError: (error) => {
+        console.error('Authentication error:', error);
+    }
+};
+
+window.AUTH_CONFIG = AUTH_CONFIG;
+window.ALLOWED_EMAILS = '${ALLOWED_EMAILS}'.split(',').map(e => e.trim());
+JSEOF
+
+echo "Generated auth-config.js with API_BASE_URL=${API_BASE_URL}"