Implement quick-add registry (task 21)

- Add url field to QuickAddAction; make action optional
- Add getQuickAdds() + SerializedQuickAddItem to registry so quick-add
  data can cross the server→client RSC boundary without serializing fns
- Update calendar/lists/notes manifests with navigation URLs
- QuickAddProvider wraps root layout: holds sheet/palette open state and
  global cmd/ctrl+k shortcut
- QuickAddSheet: bottom drawer on mobile, right-side popover on desktop,
  actions grouped by module
- CommandPalette: cmdk-powered modal with fuzzy filter and full keyboard
  nav (arrows + enter + esc)
- QuickAddFab: client button replacing the plain + stub in the dashboard
- Add .claude/** to ESLint ignores to prevent stale worktree artifacts
  from failing lint

All 4 E2E specs pass; typecheck, lint, and build clean.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/modules/calendar/manifest.tsx

@@ -156,13 +156,13 @@ const manifest: ModuleManifest = {
       id: "calendar.new-event",
       label: "New event",
       icon: "calendar-plus",
-      action: () => undefined,
+      url: "/calendar",
     },
     {
       id: "calendar.new-calendar",
       label: "New calendar",
       icon: "calendar-days",
-      action: () => undefined,
+      url: "/calendar",
     },
   ],
 };