feat(front) : ajustements layout maquette (sidebar, marges, titres)

- sidebar deplie a 232px (repli 72px conserve)
- marge horizontale du contenu responsive, 170px des xl (1280px)
- gap navbar -> contenu de 47px
- composant partage PageHeader (titre 32px/600, marge basse 44px, slot actions)
- migration des 6 pages vers PageHeader, suppression des marges hautes redondantes

frontend/modules/sites/pages/admin/sites.vue

@@ -1,22 +1,20 @@
 <template>
     <div>
-        <!-- En-tete -->
-        <div class="flex items-center justify-between">
-            <h1 class="text-xl font-bold text-primary-500 sm:text-2xl">
-                {{ t('admin.sites.title') }}
-            </h1>
-            <MalioButton
-                v-if="can('sites.manage')"
-                :label="t('admin.sites.newSite')"
-                icon-name="mdi:add-bold"
-                icon-position="left"
-                @click="openCreateDrawer"
-            />
-        </div>
+        <PageHeader>
+            {{ t('admin.sites.title') }}
+            <template #actions>
+                <MalioButton
+                    v-if="can('sites.manage')"
+                    :label="t('admin.sites.newSite')"
+                    icon-name="mdi:add-bold"
+                    icon-position="left"
+                    @click="openCreateDrawer"
+                />
+            </template>
+        </PageHeader>
 
         <!-- Table des sites -->
         <MalioDataTable
-            class="mt-6"
             :columns="columns"
             :items="siteItems"
             :total-items="sites.length"