refactor(config): 服务地址改为 dev/prod 配置文件与单个环境开关

启动时按环回、局域网、公网顺序探测地址，换网络后会静默切到别处，排查
困难。改为代码内一个布尔开关选择环境，地址分别放在 dev_config.dart 与
prod_config.dart，不再探测；调试条改地址后直接重载，不再重新探测。
release 构建若仍是开发开关会启动即报错，避免线上包连开发机。

lib/core/config/server_endpoint.dart

@@ -22,16 +22,9 @@ abstract final class ServerEndpoint {
     return value.replaceFirst(RegExp(r'/+$'), '');
   }
 
-  /// Resolves runtime > dart-define > default using normalized valid values.
-  static String resolve({
-    required String? stored,
-    required String compiled,
-    required String fallback,
-  }) {
-    return normalize(stored) ??
-        normalize(compiled) ??
-        normalize(fallback) ??
-        fallback;
+  /// 运行时手改优先，其次构建期默认地址；两者都必须先通过规范校验。
+  static String resolve({required String? stored, required String fallback}) {
+    return normalize(stored) ?? normalize(fallback) ?? fallback;
   }
 
   /// Loads the persisted override before the app creates its ApiClient.
@@ -46,11 +39,7 @@ abstract final class ServerEndpoint {
       final prefs = preferences ?? SharedPreferencesAsync();
       final stored = await prefs.getString(preferenceKey);
       AppConfig.applyRuntimeBaseUrl(
-        resolve(
-          stored: stored,
-          compiled: AppConfig.compiledBaseUrl,
-          fallback: AppConfig.defaultBaseUrl,
-        ),
+        resolve(stored: stored, fallback: AppConfig.baseUrl),
       );
     } catch (_) {
       AppConfig.clearRuntimeBaseUrl();