feat(home): add prominent "New note" button to dashboard

Add a big "New note" action to the Home screen that creates a new page
and opens it. Since the home screen has no active space, the target
space is resolved from the user's writable spaces (CASL Manage/Page
gate, mirroring the space sidebar): created directly when there is one
writable space, picked from a dropdown when there are several, hidden
when there are none. Menu items are disabled while a create is in
flight to avoid duplicate pages.

- New component features/home/components/new-note-button.tsx
- Render it at the top of pages/dashboard/home.tsx (above the carousel)
- Add i18n keys "New note" / "Create in space" to en-US and ru-RU

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/client/public/locales/ru-RU/translation.json

@@ -119,6 +119,8 @@
   "Name": "Имя",
   "New email": "Новый электронный адрес",
   "New page": "Новая страница",
+  "New note": "Новая заметка",
+  "Create in space": "Создать в пространстве",
   "New password": "Новый пароль",
   "No group found": "Группа не найдена",
   "No page history saved yet.": "История страниц ещё не сохранена.",