feat(help-center): add help panel to sidebar icon bar

New help-center module adds a question-mark icon to the sidebar with
an aside panel containing three sections: Documentation (permission-
gated links to docs viewer and API docs), Keyboard Shortcuts (inline
reference from HotkeyService with Mac/Win variants), and About
(application info). Visible to all logged-in users — individual
resource links respect existing permissions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

modules/help-center/lib/Module/HelpCenter/HelpCenterContainerRegistrar.php

@@ -0,0 +1,14 @@
+<?php
+
+namespace MintyPHP\Module\HelpCenter;
+
+use MintyPHP\App\AppContainer;
+use MintyPHP\App\Container\ContainerRegistrar;
+
+final class HelpCenterContainerRegistrar implements ContainerRegistrar
+{
+    public function register(AppContainer $container): void
+    {
+        // No services to register — help panel uses static utility classes only.
+    }
+}