fix: resolve flutter analyze errors - remove leaked code, fix method calls, cleanup imports

lib/core/config/app_config.dart

@@ -0,0 +1,13 @@
+class AppConfig {
+  AppConfig._();
+
+  static const String baseUrl = String.fromEnvironment(
+    'BASE_URL',
+    defaultValue: 'https://localhost:3000',
+  );
+
+  static const String googleClientId = String.fromEnvironment(
+    'GOOGLE_CLIENT_ID',
+    defaultValue: '',
+  );
+}