Add a maintenance pause/resume switch and a proper user navbar

RoundConfig gets a paused flag toggled via new POST /admin/pause and
/admin/resume endpoints (audit-logged, surfaced as a "Manutenzione" card in
the admin Parametri view). Pausing only stops the *next* round from opening
once the current one closes — rounds/service.py:open_new_round_if_needed
still lets an in-progress round finish, draw, and pay out its winner
normally. GET /rounds/current exposes lottery_paused so the user page shows
a maintenance banner (even while logged out) instead of silently going idle.

Also replaces the user dashboard's stacked account-bar card + bento-grid
menu with a single sticky navbar (identity row + Deposito/Bet/Prelievo
tabs), and moves the page content into a dedicated .app-shell container so
the navbar itself can span full width.

app/static/admin.html

@@ -77,6 +77,12 @@
   }
   .chain-block { color: var(--color-muted-foreground); font-size: 0.82rem; white-space: nowrap; }
 
+  .row-between { display: flex; align-items: center; justify-content: space-between; gap: 12px; }
+  #maintenance-btn.btn-stop {
+    background: var(--color-destructive-bg); color: var(--color-destructive); border-color: var(--color-destructive);
+  }
+  .status-dot.status-paused { background: var(--color-destructive); }
+
   main { max-width: 960px; margin: 0 auto; padding: 24px 20px 80px; }
 
   .view { display: none; }
@@ -221,6 +227,21 @@
       <h2 class="section-title">Parametri</h2>
       <p class="hint">Configurazione operativa, salvata nel database — modificabile in qualsiasi momento senza riavviare il server.</p>
 
+      <div class="card" id="maintenance-card">
+        <h2>Manutenzione</h2>
+        <p class="hint" id="maintenance-hint">
+          Interrompe l'apertura di nuovi round dopo quello in corso, senza troncare il round attuale — chiusura,
+          estrazione e pagamento del vincitore avvengono normalmente. Gli utenti vedono un avviso di manutenzione.
+        </p>
+        <div class="row-between">
+          <span class="chain-status-pill">
+            <span class="status-dot" id="maintenance-dot"></span>
+            <span id="maintenance-status-label">—</span>
+          </span>
+          <button id="maintenance-btn" class="secondary" style="width:auto;margin-top:0" onclick="toggleMaintenance()">…</button>
+        </div>
+      </div>
+
       <div class="card">
         <div class="grid-2">
           <div>
@@ -460,11 +481,53 @@ async function adminLoadConfig() {
     document.getElementById('admin-min-amount').value = data.min_amount_sats / SATS_PER_PLM;
     document.getElementById('admin-fee-rate').value = data.fee_rate_sat_vb;
     document.getElementById('admin-rbf-timeout').value = data.rbf_timeout_seconds;
+    renderMaintenanceState(data.paused);
   } catch (e) {
     toast('Errore nel caricamento configurazione: ' + e.message, 'error');
   }
 }
 
+function renderMaintenanceState(paused) {
+  const dot = document.getElementById('maintenance-dot');
+  const label = document.getElementById('maintenance-status-label');
+  const btn = document.getElementById('maintenance-btn');
+  btn.dataset.paused = paused ? '1' : '0';
+  if (paused) {
+    dot.className = 'status-dot status-paused';
+    label.textContent = 'In pausa: nessun nuovo round verrà aperto';
+    btn.textContent = 'Riprendi lotteria';
+    btn.classList.remove('btn-stop');
+  } else {
+    dot.className = 'status-dot status-open';
+    label.textContent = 'Attiva: i round si susseguono normalmente';
+    btn.textContent = 'Interrompi dopo questo round';
+    btn.classList.add('btn-stop');
+  }
+}
+
+async function toggleMaintenance() {
+  const btn = document.getElementById('maintenance-btn');
+  const isPaused = btn.dataset.paused === '1';
+  const path = isPaused ? '/admin/resume' : '/admin/pause';
+  if (!isPaused && !window.confirm(
+    "Nessun nuovo round verrà aperto dopo quello in corso, fino a quando non riprendi la lotteria. " +
+    "Il round attuale (se presente) verrà comunque completato e il vincitore pagato. Continuare?"
+  )) {
+    return;
+  }
+  btn.disabled = true;
+  try {
+    const data = await callAdmin('POST', path, {});
+    renderMaintenanceState(data.paused);
+    toast(data.paused ? 'Lotteria in pausa.' : 'Lotteria ripresa.', 'success');
+    refreshChainStatus();
+  } catch (e) {
+    toast('Errore: ' + e.message, 'error');
+  } finally {
+    btn.disabled = false;
+  }
+}
+
 async function adminSave() {
   const btn = document.getElementById('save-btn');
   const feeAddress = document.getElementById('admin-fee-address').value;