feat(frontend) : admin middleware, fix avatar upload, centralize IRI extraction, remove Nitro proxy

- Add admin middleware protecting /admin page (ROLE_ADMIN check)
- Fix useAvatarService to use useApi() with FormData detection
- Create extractIdFromIri() utility, replace manual IRI parsing
- Remove redundant Nitro devProxy (Vite proxy handles dev)

Tickets: T-014, T-015, T-017, T-021

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

frontend/pages/admin.vue

@@ -35,6 +35,7 @@
 </template>
 
 <script setup lang="ts">
+definePageMeta({ middleware: ['admin'] })
 useHead({ title: 'Administration' })
 
 const tabs = [

frontend/pages/portal/index.vue

@@ -53,10 +53,8 @@ const ticketCountByProject = computed(() => {
     const counts: Record<number, number> = {}
     for (const ticket of tickets.value) {
         if (ticket.status === 'new' || ticket.status === 'in_progress') {
-            // Extract project ID from IRI
-            const match = ticket.project.match(/\/api\/projects\/(\d+)/)
-            if (match) {
-                const projectId = Number(match[1])
+            const projectId = extractIdFromIri(ticket.project)
+            if (projectId) {
                 counts[projectId] = (counts[projectId] ?? 0) + 1
             }
         }