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_lists.go

@@ -167,8 +167,8 @@ func (s *Server) handleCreateListItem(w http.ResponseWriter, r *http.Request) {
 }
 
 // setListItemDone checks an item off (or back on) and tells the list's viewers. Shared by
-// PATCH /lists/{id}/items/{itemId} and the MCP tool check_list_item; access is checked first.
-func (s *Server) setListItemDone(userID, listID, itemID string, done bool) (*domain.ListItem, error) {
+// PATCH /lists/{id}/items/{itemId} and the MCP tool check_list_item (byAgent); access is checked first.
+func (s *Server) setListItemDone(userID, listID, itemID string, done, byAgent bool) (*domain.ListItem, error) {
 	if err := s.store.EnsureListItemsWritable(userID, listID, itemID); err != nil {
 		return nil, err
 	}
@@ -181,6 +181,7 @@ func (s *Server) setListItemDone(userID, listID, itemID string, done bool) (*dom
 	if err != nil {
 		return nil, err
 	}
+	item.AgentMark = s.store.SetListItemAgentMark(itemID, byAgent)
 	s.wsHub.BroadcastListEvent(listID, "ITEM_TOGGLED", item)
 	return item, nil
 }
@@ -201,7 +202,7 @@ func (s *Server) handleToggleListItem(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	item, err := s.setListItemDone(userID, listID, itemID, req.IsCompleted)
+	item, err := s.setListItemDone(userID, listID, itemID, req.IsCompleted, false)
 	if err != nil {
 		writeError(w, http.StatusBadRequest, err.Error())
 		return
@@ -231,6 +232,7 @@ func (s *Server) handleUpdateListItem(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, err.Error())
 		return
 	}
+	item.AgentMark = s.store.SetListItemAgentMark(itemID, false)
 
 	s.wsHub.BroadcastListEvent(listID, "ITEM_UPDATED", item)
 	writeJSON(w, http.StatusOK, item)