fix: remove an agent's forward rules with the agent (0.0.4)

Deleting a machine left its forward rules behind: the host ports stayed
bound and "busy" with no page to remove them from. The rules, their
listeners and ufw rules now go with the agent, and rules orphaned by
older versions are dropped on start.

A host port equal to the direct tunnel port gets its own message.

internal/server/handlers_panel_fwd.go

@@ -18,6 +18,7 @@ func (s *Server) handleForwardsPage(w http.ResponseWriter, r *http.Request) {
 	rules, _ := s.db.ListForwardRulesByAgent(id)
 	errMsg := map[string]string{
 		"busy":   "Этот порт хоста уже занят другим правилом.",
+		"tunnel": "Этот порт занят прямым туннелем панели (см. Настройки).",
 		"port":   "Некорректный номер порта.",
 		"listen": "Не удалось занять порт на хосте (возможно, уже используется).",
 		"db":     "Ошибка базы данных.",
@@ -76,7 +77,11 @@ func (s *Server) handleForwardAdd(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	// Reject a host port already bound by another forward rule or the tunnel.
-	if s.db.HostPortUsed(hostPort) || hostPort == s.TunnelPort() {
+	if hostPort == s.TunnelPort() {
+		http.Redirect(w, r, "/agents/"+id+"/forwards?err=tunnel", http.StatusSeeOther)
+		return
+	}
+	if s.db.HostPortUsed(hostPort) {
 		http.Redirect(w, r, "/agents/"+id+"/forwards?err=busy", http.StatusSeeOther)
 		return
 	}
@@ -107,14 +112,19 @@ func (s *Server) handleForwardDelete(w http.ResponseWriter, r *http.Request) {
 	}
 	rid, _ := strconv.ParseInt(r.PathValue("rid"), 10, 64)
 	rule, _ := s.db.GetForwardRule(rid)
-	s.fwd.close(rid)
-	_ = s.db.DeleteForwardRule(rid)
-	// Remove the ufw rule bound to this forward rule (the shared tunnel port
-	// stays while another direct forward needs it).
-	s.ufw.revokeForRule(rid)
+	s.removeForward(rid)
 	dest := "/"
 	if rule != nil {
 		dest = "/agents/" + rule.AgentID + "/forwards"
 	}
 	http.Redirect(w, r, dest, http.StatusSeeOther)
 }
+
+// removeForward closes a forward rule's listener and deletes the rule, along
+// with the ufw rule bound to it (the shared tunnel port stays while another
+// direct forward needs it).
+func (s *Server) removeForward(rid int64) {
+	s.fwd.close(rid)
+	_ = s.db.DeleteForwardRule(rid)
+	s.ufw.revokeForRule(rid)
+}