Restructure citizen vote page + add vote deadline

Reorganize the citizen page (/commune/[slug]) for voters: full-width
interactive chart with "Population" zoom by default, separate auth and
vote sections, countdown timer for vote deadline.

Backend: add vote_deadline column to communes with Alembic migration.
Admin: add deadline configuration card with datetime-local input.

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

frontend/app/pages/admin/communes/[slug]/index.vue

@@ -29,6 +29,29 @@
       </NuxtLink>
     </div>
 
+    <!-- Vote deadline -->
+    <div class="card" style="margin-bottom: 2rem;">
+      <h3 style="margin-bottom: 1rem;">Parametres du vote</h3>
+      <div style="display: flex; gap: 1rem; align-items: flex-end; flex-wrap: wrap;">
+        <div>
+          <label style="display: block; font-size: 0.8rem; color: var(--color-text-muted); margin-bottom: 0.25rem;">
+            Date limite de vote
+          </label>
+          <input
+            v-model="voteDeadline"
+            type="datetime-local"
+            class="form-input"
+            style="width: 260px;"
+          />
+        </div>
+        <button class="btn btn-primary" @click="saveDeadline" :disabled="savingDeadline">
+          <span v-if="savingDeadline" class="spinner" style="width: 1rem; height: 1rem;"></span>
+          Enregistrer
+        </button>
+        <span v-if="deadlineSaved" style="color: #059669; font-size: 0.85rem;">Enregistre !</span>
+      </div>
+    </div>
+
     <!-- Stats -->
     <div v-if="stats" class="card" style="margin-bottom: 2rem;">
       <h3 style="margin-bottom: 1rem;">Statistiques foyers</h3>
@@ -145,6 +168,26 @@ const search = ref('')
 const page = ref(1)
 const perPage = 20
 
+// Vote deadline
+const voteDeadline = ref('')
+const savingDeadline = ref(false)
+const deadlineSaved = ref(false)
+
+async function saveDeadline() {
+  savingDeadline.value = true
+  deadlineSaved.value = false
+  try {
+    await api.put(`/communes/${slug}`, {
+      vote_deadline: voteDeadline.value ? new Date(voteDeadline.value).toISOString() : null,
+    })
+    deadlineSaved.value = true
+  } catch (e: any) {
+    alert(e.message || 'Erreur')
+  } finally {
+    savingDeadline.value = false
+  }
+}
+
 const filteredHouseholds = computed(() => {
   if (!search.value) return households.value
   const q = search.value.toLowerCase()
@@ -173,6 +216,10 @@ function statusBadge(status: string) {
 onMounted(async () => {
   try {
     commune.value = await api.get<any>(`/communes/${slug}`)
+    if (commune.value.vote_deadline) {
+      // Format for datetime-local input (YYYY-MM-DDTHH:mm)
+      voteDeadline.value = commune.value.vote_deadline.slice(0, 16)
+    }
   } catch (e: any) {
     return
   }