feat: Phase 6 - MCP + Webhooks + Worker + Polish

- MCP server: stateless JSON-RPC 2.0 with 18 tools (tasks, habits, projects, notes, domains, search, activity)
- Webhooks API: CRUD routes under /api/domains/[domainId]/webhooks/ with test endpoint and deliveries log
- Webhook delivery: HMAC-SHA256 signed POST with retry (exponential backoff, max 6)
- Worker rewrite: Drizzle ORM instead of PocketBase, polls jobs table, handles webhook_delivery, recurring_spawn, ai_dispatch
- Rate limiting: token bucket per IP/API key (100 req/min REST, 300 req/min MCP)
- Keyboard help overlay: ? opens Radix Dialog with search/filter, Esc closes
- AI @mention stub: @agent in command palette dispatches CustomEvent
- Mobile responsive: bottom nav, single-column kanban, day view calendar, 44px touch targets
- Accessibility: skip-to-content link, focus rings, aria-labels, color contrast
- E2E tests: mcp.spec.ts, webhooks.spec.ts, realtime.spec.ts added
- Schema: api_keys and webhook_deliveries tables with migration
- Removed old PocketBase-style database.ts from worker

apps/web/components/command-palette.tsx

@@ -84,6 +84,11 @@ export function CommandPalette() {
     { label: 'New habit', action: () => router.push('/habits?new=true') },
     { label: 'New project', action: () => router.push('/projects?new=true') },
     { label: 'New note', action: () => router.push('/notes?new=true') },
+    { label: 'Ask AI agent...', shortcut: '@', action: () => {
+      setOpen(false);
+      // Dispatch event for AI dispatch flow
+      document.dispatchEvent(new CustomEvent('open-ai-dispatch'));
+    }},
   ];
 
   // Search handler