fix(page-templates): show a template marker icon in the page tree (#38)

Template pages were toggleable but indistinguishable in the sidebar tree.
Render an IconTemplate next to the title when node.isTemplate is true, wrapped
in a Tooltip(label='Template') with an aria-label + role='img' for AT. The
icon is a child of the row Link so clicks navigate as normal; pointer events
stay enabled so the tooltip's hover handlers fire. Adds the 'Template' i18n
key to en-US and ru-RU (other locales fall back to en-US).

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

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

@@ -183,6 +183,7 @@
   "Successfully imported": "Успешно импортировано",
   "Successfully restored": "Успешно восстановлено",
   "System settings": "Системные настройки",
+  "Template": "Шаблон",
   "Templates": "Шаблоны",
   "Theme": "Тема",
   "To change your email, you have to enter your password and new email.": "Чтобы изменить электронную почту, вам нужно ввести пароль и новый адрес.",