web: reset links to the default mode, and keep CN agents dial-only by default [CI]

POST /api/admin/links/reset clears every manual link setting and turns automatic linking on. In the default rules a listening node in CN ranks below a listening node elsewhere, so the CN side dials; the links are pushed again when a node's country is first resolved or changes.

backend/src/MoShiro.Backend.Application/Agents/AgentService.cs

@@ -80,6 +80,8 @@ public sealed partial class AgentService
         _gateway = gateway;
         _planner = planner;
         _settings = settings;
+        // 线路的默认方向看国家（国内的节点默认只拨出）：国家查到或变了就重新下发
+        _nodes.OnCountryChanged = () => AfterAgentSetChangedAsync(CancellationToken.None);
     }
 
     public async ValueTask<IReadOnlyList<AgentView>> ListAsync(CancellationToken ct)