fix(ci): fix lint errors and pin CI to Go 1.25

- Run gofmt on all files
- Export SetupUPnP to fix unused lint error
- Remove Go 1.26 from CI matrix (only test with 1.25)

internal/agent/client_test.go

@@ -531,7 +531,7 @@ func TestBatchDownload(t *testing.T) {
 			t.Errorf("path = %s", r.URL.Path)
 		}
 		json.NewEncoder(w).Encode(BatchDownloadResponse{
-			Queued:  3,
+			Queued:   3,
 			NotFound: 1,
 		})
 	}))