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/components/AgentBadge.tsx

@@ -0,0 +1,33 @@
+import React from 'react';
+import { Bot } from 'lucide-react';
+import { AgentMark } from '../lib/types';
+
+interface AgentBadgeProps {
+  mark: AgentMark | undefined;
+  // sm: task rows and the task detail; xs: Kanban cards and list items
+  size?: 'sm' | 'xs';
+}
+
+const TITLES: Record<AgentMark, string> = {
+  created: 'Von einem KI-Agenten per MCP angelegt. Das Zeichen verschwindet, sobald du den Eintrag selbst änderst.',
+  edited: 'Zuletzt von einem KI-Agenten per MCP geändert. Das Zeichen verschwindet, sobald du den Eintrag selbst änderst.',
+};
+
+// Marks entries an AI agent created or changed via MCP that the user has not touched since
+// (Doku/ui-patterns.md)
+export const AgentBadge: React.FC<AgentBadgeProps> = ({ mark, size = 'sm' }) => {
+  if (mark !== 'created' && mark !== 'edited') return null;
+  const label = mark === 'created' ? 'KI' : 'KI geändert';
+  return (
+    <span
+      className={`px-1.5 border border-accent/40 bg-accent/10 text-accent rounded-btn font-medium inline-flex items-center gap-1 flex-shrink-0 ${
+        size === 'xs' ? 'py-0.2 text-[9px]' : 'py-0.5 text-[10px]'
+      }`}
+      title={TITLES[mark]}
+      aria-label={TITLES[mark]}
+    >
+      <Bot className="w-2.5 h-2.5" />
+      <span>{label}</span>
+    </span>
+  );
+};

frontend/src/components/__tests__/AgentBadge.test.tsx

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+import { describe, it, expect } from 'vitest';
+import { render } from '@testing-library/react';
+import { AgentBadge } from '../AgentBadge';
+
+describe('AgentBadge', () => {
+  it('shows nothing for entries of the user', () => {
+    expect(render(<AgentBadge mark={undefined} />).container.firstChild).toBeNull();
+  });
+
+  it('tells created and edited entries apart', () => {
+    const created = render(<AgentBadge mark="created" />).container.firstChild as HTMLElement;
+    expect(created.textContent).toBe('KI');
+    expect(created.getAttribute('title')).toContain('angelegt');
+    const edited = render(<AgentBadge mark="edited" />).container.firstChild as HTMLElement;
+    expect(edited.textContent).toBe('KI geändert');
+    expect(edited.getAttribute('title')).toContain('geändert');
+  });
+});