fix: surface frps startup failures and avoid nginx port conflicts

internal/frp/agent_installer_test.go

@@ -0,0 +1,13 @@
+package frp
+
+import "testing"
+
+func TestExtractAgentVersion(t *testing.T) {
+	output := "agent version: 0.15.1\nhavline-agent installed\nToken: abc123"
+	if got := extractAgentVersion(output); got != "0.15.1" {
+		t.Fatalf("版本解析失败，got %q", got)
+	}
+	if got := extractAgentVersion("havline-agent installed\nToken: abc123"); got != "" {
+		t.Fatalf("无版本行时应返回空串，got %q", got)
+	}
+}