feat(activity-log) : add global activity log page with filters and pagination

New /activity-log page showing all audit entries across pieces, products
and composants. Includes entity type and action filters, expandable
diffs, clickable entity links and pagination. Navbar link added under
Ressources liées.

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

app/components/layout/AppNavbar.vue

@@ -275,11 +275,12 @@ const navGroups: NavGroup[] = [
   {
     id: 'resources',
     label: 'Ressources liées',
-    activePaths: ['/sites', '/documents', '/constructeurs'],
+    activePaths: ['/sites', '/documents', '/constructeurs', '/activity-log'],
     children: [
       { to: '/sites', label: 'Sites' },
       { to: '/documents', label: 'Documents' },
       { to: '/constructeurs', label: 'Fournisseurs' },
+      { to: '/activity-log', label: 'Journal d\'activité' },
     ],
   },
 ]