feat(permissions) : add role-based UI guards and readonly mode for viewers

- Add usePermissions composable (isAdmin, canEdit, canView)
- Password-protected profile login with modal on profiles page
- Disable all form fields for ROLE_VIEWER across edit/create pages
- Show navigation buttons (Modifier/Consulter) for all roles, hide delete for viewers
- Add readonly prop to ModelTypeForm for category pages
- Disable modal fields (sites, constructeurs) for viewers
- Guard /admin routes in middleware

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

app/pages/sites.vue

@@ -11,7 +11,7 @@
         <h2 class="text-2xl font-bold">
           Sites
         </h2>
-        <button class="btn btn-primary" @click="openCreateSiteModal">
+        <button v-if="canEdit" class="btn btn-primary" @click="openCreateSiteModal">
           <IconLucidePlus class="w-5 h-5 mr-2" aria-hidden="true" />
           Ajouter un site
         </button>
@@ -30,7 +30,7 @@
           <p class="text-gray-500 mb-4">
             Commencez par ajouter votre premier site.
           </p>
-          <button class="btn btn-primary" @click="openCreateSiteModal">
+          <button v-if="canEdit" class="btn btn-primary" @click="openCreateSiteModal">
             Ajouter un site
           </button>
         </div>
@@ -50,6 +50,7 @@
     <SiteCreateModal
       :visible="showAddSiteModal"
       :site="newSite"
+      :disabled="!canEdit"
       @close="closeCreateModal"
       @submit="handleCreateSite"
     />
@@ -64,6 +65,7 @@
       :can-preview-document="canPreviewDocument"
       :document-icon="documentIcon"
       :format-size="formatSize"
+      :disabled="!canEdit"
       @close="closeEditModal"
       @submit="handleUpdateSite"
       @remove-document="handleRemoveSiteDocument"
@@ -83,6 +85,8 @@ import SiteCreateModal from '~/components/sites/SiteCreateModal.vue'
 import SiteEditModal from '~/components/sites/SiteEditModal.vue'
 import { useSiteManagement } from '~/composables/useSiteManagement'
 
+const { canEdit } = usePermissions()
+
 const {
   sites,
   loading,