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>

frontend/package.json

@@ -1,7 +1,7 @@
 {
   "name": "mindsift-frontend",
   "private": true,
-  "version": "0.28.0",
+  "version": "0.29.0",
   "license": "Unlicense",
   "type": "module",
   "scripts": {