fix(config): 指定 API_BASE_URL 时跳过地址探测

lib/core/config/app_config.dart

@@ -85,7 +85,15 @@ class AppConfig {
   static Future<void> probeAndApplyBaseUrl({
     Future<bool> Function(String baseUrl)? probe,
     String? fallbackBaseUrl,
+
+    /// 编译期地址测试注入；未传时读取 `API_BASE_URL`。
+    String? compiledOverride,
   }) async {
+    final compiled = compiledOverride ?? compiledBaseUrl;
+    if (compiled.isNotEmpty) {
+      if (_runtimeBaseUrl.isEmpty) applyRuntimeBaseUrl(compiled);
+      return;
+    }
     final candidates = <String>[
       if (_runtimeBaseUrl.isNotEmpty) _runtimeBaseUrl,
       for (final candidate in _probeCandidates)