Add development documentation and enhance SPA navigation with category/item detail views

- Add DEVELOPMENT.md with complete LXC environment setup guide
- Implement dynamic category tree with item navigation in sidebar
- Add category detail view with items list via AJAX
- Add item edit form with delete functionality
- Enhance SPA routing to support query parameters for categories/items
- Update Bootstrap styling with icons and improved navigation
- Include SQLite database in repository for development

config.php

@@ -46,6 +46,6 @@ $twig->addGlobal('app_name', APP_NAME);
 $twig->addGlobal('delete_part_confirm', $translator->trans('Are you sure you want to delete this part?'));
 $twig->addGlobal('delete_category_confirm', $translator->trans('Are you sure you want to delete this category?'));
 
-// Build category tree for sidebar
-$sidebarHtml = '<ul class="nav flex-column nav-pills"><li class="nav-item"><a class="nav-link" href="#" data-route="/">Overview</a></li><li class="nav-item"><a class="nav-link" href="#" data-route="/categories">Categories</a></li><li class="nav-item"><a class="nav-link" href="#" data-route="/parts">Parts</a></li></ul>';
+// Sidebar will be built dynamically via AJAX
+$sidebarHtml = '<div id="sidebar-tree">Loading...</div>';
 $twig->addGlobal('sidebar_html', $sidebarHtml);