feat: 切换邮箱认证并重构前后端启动与门禁

apps/lib/core/config/env.dart

@@ -0,0 +1,17 @@
+import 'dart:io';
+
+class Env {
+  static String get backendUrl {
+    final injected = const String.fromEnvironment('BACKEND_URL');
+    if (injected.isNotEmpty && injected != 'false') {
+      return injected;
+    }
+
+    if (Platform.isAndroid) {
+      return 'http://10.0.2.2:5775';
+    }
+    return 'http://localhost:5775';
+  }
+
+  static Future<void> init() async {}
+}