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_thoughts.go

@@ -245,6 +245,8 @@ type taskPatch struct {
 	Tags         *[]string         `json:"tags"`
 	Assignees    *[]string         `json:"assignees"`
 	Recurrence   *string           `json:"recurrence"`
+	// byAgent: the change comes from an AI agent (MCP) and marks the task; otherwise the mark goes
+	byAgent bool
 }
 
 // updateTask applies a patch, keeps a linked note block in step, tells everyone who sees the task
@@ -261,6 +263,7 @@ func (s *Server) updateTask(userID, thoughtID string, req taskPatch) (*domain.Th
 	if err != nil {
 		return nil, err
 	}
+	updated.AgentMark = s.store.SetThoughtAgentMark(thoughtID, updated.AgentMark, req.byAgent)
 	if req.Assignees != nil {
 		assignees, err := s.store.SetTaskAssignees(userID, thoughtID, *req.Assignees)
 		if err != nil {
@@ -305,23 +308,30 @@ func (s *Server) handleUnlinkEnhancedTask(w http.ResponseWriter, r *http.Request
 	writeJSON(w, http.StatusOK, map[string]bool{"unlinked": true})
 }
 
-func (s *Server) handleDeleteThought(w http.ResponseWriter, r *http.Request) {
-	userID := auth.GetUserID(r.Context())
-	thoughtID := chi.URLParam(r, "id")
+// deleteTask removes a task, tells everyone who saw it and notifies its watchers. Shared by
+// DELETE /thoughts/{id} and the MCP tool delete_task.
+func (s *Server) deleteTask(userID, thoughtID string) error {
 	th, err := s.store.GetThoughtByID(userID, thoughtID)
 	if err == nil && th.TaskListID != "" && !s.store.CanEditTaskList(userID, th.TaskListID) {
-		writeError(w, http.StatusForbidden, storage.ErrTaskListReadOnly.Error())
-		return
+		return storage.ErrTaskListReadOnly
 	}
 	audience := s.taskAudience(th)
 	if err := s.store.DeleteThought(userID, thoughtID); err != nil {
-		writeStoreError(w, http.StatusInternalServerError, err)
-		return
+		return err
 	}
 	if th != nil {
 		s.notifyTaskChange(userID, th, nil, true)
 	}
 	s.wsHub.BroadcastToUsers(audience, "TASK_DELETED", map[string]string{"id": thoughtID})
+	return nil
+}
+
+func (s *Server) handleDeleteThought(w http.ResponseWriter, r *http.Request) {
+	userID := auth.GetUserID(r.Context())
+	if err := s.deleteTask(userID, chi.URLParam(r, "id")); err != nil {
+		writeStoreError(w, http.StatusInternalServerError, err)
+		return
+	}
 	writeJSON(w, http.StatusOK, map[string]bool{"deleted": true})
 }