feat(ui): add outline/fill icon-swap pattern for aside icon bar

Introduce data-icon-swap attribute with paired outline/fill <i> elements.
CSS toggles to filled icon on hover and active state. Module slots
auto-derive fill variant from icon name, with explicit icon_fill override
for icons without a fill counterpart (e.g. bi-headset). Add enforcement
script bin/icon-swap-check.sh.

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

modules/helpdesk/module.php

@@ -49,6 +49,7 @@ return [
                 'key' => 'helpdesk',
                 'label' => 'Helpdesk',
                 'icon' => 'bi-headset',
+                'icon_fill' => 'bi-headset',
                 'href' => '',
                 'permission' => 'helpdesk.access',
                 'panel_template' => 'templates/aside-helpdesk-panel.phtml',