Add Update Manager for automated Part-DB updates

This feature adds a comprehensive Update Manager similar to Mainsail's
update system, allowing administrators to update Part-DB directly from
the web interface.

Features:
- Web UI at /admin/update-manager showing current and available versions
- Support for Git-based installations with automatic update execution
- Maintenance mode during updates to prevent user access
- Automatic database backup before updates
- Git rollback points for recovery (tags created before each update)
- Progress tracking with real-time status updates
- Update history and log viewing
- Downgrade support with appropriate UI messaging
- CLI command `php bin/console partdb:update` for server-side updates

New files:
- UpdateManagerController: Handles all web UI routes
- UpdateCommand: CLI command for running updates
- UpdateExecutor: Core update execution logic with safety mechanisms
- UpdateChecker: GitHub API integration for version checking
- InstallationTypeDetector: Detects installation type (Git/Docker/ZIP)
- MaintenanceModeSubscriber: Blocks user access during maintenance
- UpdateExtension: Twig functions for update notifications

UI improvements:
- Update notification in navbar for admins when update available
- Confirmation dialogs for update/downgrade actions
- Downgrade-specific text throughout the interface
- Progress page with auto-refresh

src/Services/Trees/ToolsTreeBuilder.php

@@ -315,6 +315,13 @@ class ToolsTreeBuilder
             ))->setIcon('fa fa-fw fa-gears fa-solid');
         }
 
+        if ($this->security->isGranted('@system.show_updates')) {
+            $nodes[] = (new TreeViewNode(
+                $this->translator->trans('tree.tools.system.update_manager'),
+                $this->urlGenerator->generate('admin_update_manager')
+            ))->setIcon('fa-fw fa-treeview fa-solid fa-cloud-download-alt');
+        }
+
         return $nodes;
     }
 }