feat(mcp): delete tasks, create task lists and lists, agent badge; export/import settings category

New MCP tools delete_task (tasks:write), create_task_list (tasks:write) and create_list
(lists:write); list_task_lists now returns the board columns so agents know the valid
kanbanStatus values. Task deletion is a shared helper (deleteTask) for REST and MCP.

Tasks and list items get agent_mark (migration 12): "created" when an agent adds them via MCP,
"edited" when an agent changes them; a change by the user clears it. The new AgentBadge shows
"KI" / "KI geändert" in task rows, Kanban cards, the task detail, the inbox and lists.

Settings: export and import move out of "Webhooks, KI-Agenten & Export" into their own
category "Export & Import". Docs, help, README and changelog updated; v0.29.0.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/api/handlers_integrations.go

@@ -226,7 +226,7 @@ var errListIDRequired = errors.New("Feld 'listId' ist für Listeneinträge erfor
 
 // addListItem appends an item to a list the user may write to; the error is storage.ErrListReadOnly for
 // viewers and "not found" for lists the user cannot see.
-func (s *Server) addListItem(userID, listID, content, category, quantity string) (*domain.ListItem, error) {
+func (s *Server) addListItem(userID, listID, content, category, quantity string, byAgent bool) (*domain.ListItem, error) {
 	if strings.TrimSpace(listID) == "" {
 		return nil, errListIDRequired
 	}
@@ -237,13 +237,16 @@ func (s *Server) addListItem(userID, listID, content, category, quantity string)
 	if err != nil {
 		return nil, err
 	}
+	if byAgent {
+		item.AgentMark = s.store.MarkListItemAgentCreated(item.ID)
+	}
 	s.wsHub.BroadcastListEvent(listID, "ITEM_CREATED", item)
 	return item, nil
 }
 
 // ingestListItem adds an item to a list (scope webhook:list) the owner of the key may write to.
 func (s *Server) ingestListItem(w http.ResponseWriter, userID, listID, content, category, quantity string) {
-	item, err := s.addListItem(userID, listID, content, category, quantity)
+	item, err := s.addListItem(userID, listID, content, category, quantity, false)
 	if err != nil {
 		status := http.StatusNotFound
 		switch {