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/src/features/lists/SharedListsView.tsx

@@ -16,6 +16,7 @@ import { OFFLINE_ITEM_PREFIX, pendingListItems } from '../../lib/offline';
 import { UnifiedShareModal } from '../../components/UnifiedShareModal';
 import { AvatarStack, AvatarPerson } from '../../components/AvatarStack';
 import { CountBadge } from '../../components/CountBadge';
+import { AgentBadge } from '../../components/AgentBadge';
 import { FormSheet } from '../../components/FormSheet';
 import { useMobileActions } from '../../context/MobileActionContext';
 
@@ -1390,6 +1391,7 @@ export const SharedListsView: React.FC<SharedListsViewProps> = ({ onRefreshGloba
                             )}
                           </div>
 
+                          <AgentBadge mark={item.agentMark} size="xs" />
                           {renderItemAuthor(item)}
                           <button
                             type="button"
@@ -1499,6 +1501,7 @@ export const SharedListsView: React.FC<SharedListsViewProps> = ({ onRefreshGloba
                       </div>
 
                       <div className="flex items-center gap-2">
+                        <AgentBadge mark={item.agentMark} size="xs" />
                         {renderItemAuthor(item)}
                         {item.completedByName && (
                           <span className="text-xs text-faint">✓ {item.completedByName}</span>