feat: add Партномера nav item and summary page

- Top nav: link to /partnumber-books
- Page: summary cards (active version, unique LOTs, total PN, primary PN)
  + searchable items table for active book
  + collapsible history of all snapshots

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

web/templates/base.html

@@ -21,6 +21,7 @@
                     <div class="hidden md:flex space-x-4">
                         <a href="/projects" class="text-gray-600 hover:text-gray-900 px-3 py-2 text-sm">Мои проекты</a>
                         <a href="/pricelists" class="text-gray-600 hover:text-gray-900 px-3 py-2 text-sm">Прайслисты</a>
+                        <a href="/partnumber-books" class="text-gray-600 hover:text-gray-900 px-3 py-2 text-sm">Партномера</a>
                         <a href="/setup" class="text-gray-600 hover:text-gray-900 px-3 py-2 text-sm">Настройки</a>
                     </div>
                 </div>