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/migrations.go

@@ -32,6 +32,7 @@ var migrations = []migration{
 	{9, "Web-Push", (*Store).migratePush},
 	{10, "Registrierung und Einladungslinks", (*Store).migrateRegistration},
 	{11, "E-Mail-Bestätigung", (*Store).migrateEmailVerification},
+	{12, "Markierung für Einträge von KI-Agenten", (*Store).migrateAgentMark},
 }
 
 func (s *Store) migrate() error {