feat: 完善多模型配置与运行切换

将模型连接统一持久化管理，并支持 Agent 运行中切换模型以及中断后选择模型继续。补充配置校验、事务与前后端交互测试。

server/src/test/java/tech/easyflow/manuagent/KeyCipherAndShellTest.java

@@ -28,8 +28,8 @@ class KeyCipherAndShellTest {
 
     private AppProperties properties() {
         return new AppProperties(
-                Path.of("data"), Path.of("deepseek"), Path.of("dashscope"),
-                "unit-test-master", "admin", "admin123", "https://api.example.test", "model",
-                131_072, "smart-factory-agent-runtime:test", "bridge", Duration.ofMinutes(1));
+                Path.of("data"), Path.of("dashscope"),
+                "unit-test-master", "admin", "admin123",
+                "smart-factory-agent-runtime:test", "bridge", Duration.ofMinutes(1));
     }
 }