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/storage/docsync.go

@@ -483,7 +483,7 @@ func (s *Store) ReconcileDocTaskLinks(docID string) []string {
 // GetThoughtByIDUnchecked loads a task without access check, for server-internal notifications.
 func (s *Store) GetThoughtByIDUnchecked(thoughtID string) (*domain.Thought, error) {
 	return scanThought(s.db.QueryRow(
-		`SELECT id, user_id, content, tags, priority, source, status, is_completed, converted_type, converted_ref_id, due_date, task_list_id, kanban_status, notes, alarm_sent, created_at, triaged_at, subtasks, sort_order, recurrence
+		`SELECT id, user_id, content, tags, priority, source, status, is_completed, converted_type, converted_ref_id, due_date, task_list_id, kanban_status, notes, alarm_sent, created_at, triaged_at, subtasks, sort_order, recurrence, agent_mark
 		 FROM thoughts WHERE id = ?`, thoughtID))
 }