feat(agent): v0.3.9 sync, UI details, self-update, centralized version

- Add agent/server startup sync (sync/sync_response)
- Centralize agent version in agent/VERSION + expose /api/agent/version
- Display agent version, nodeId and server version in local UI
- Add agent self-update detection/download/restart via helper scripts
- Run start/stop/delete/reset handlers in goroutines to avoid WebSocket blocking
- Update dashboard download links and SUIVI_VPN_ONDEMAND.md
- Document Podman stays installer-managed, not agent-updated

agent/ui/index.html

@@ -479,6 +479,8 @@
       <h1 id="welcome-text">Bienvenue</h1>
       <p class="subtitle">État de ton poste</p>
 
+      <div id="update-banner"></div>
+
       <div class="services">
         <div class="service-item" id="svc-connection">
           <div class="service-icon pending">⏳</div>
@@ -628,6 +630,7 @@
             : 'Bienvenue';
           showView('dashboard');
           ws.send(JSON.stringify({action: 'instances'}));
+          loadSettings();
           break;
 
         case 'activation_failed':
@@ -671,6 +674,18 @@
         case 'config':
           fillSettings(msg.config);
           break;
+
+        case 'update_available':
+          fillSettings({
+            ...getCurrentConfig(),
+            server_version: msg.version,
+            update_available: true
+          });
+          break;
+
+        case 'update_progress':
+          showUpdateProgress(msg.percent, msg.message);
+          break;
       }
     }
 
@@ -876,7 +891,14 @@
       }
     }
 
+    let currentConfig = {};
+
+    function getCurrentConfig() {
+      return currentConfig;
+    }
+
     function fillSettings(cfg) {
+      currentConfig = cfg;
       document.getElementById('cfg-server').value = cfg.server || '';
       document.getElementById('cfg-node').value = cfg.node_id || '';
       document.getElementById('cfg-headscale-url').value = cfg.headscale_url || '';
@@ -885,6 +907,46 @@
       document.getElementById('detail-version').textContent = cfg.version || 'dev';
       document.getElementById('detail-nodeid').textContent = cfg.node_id || '-';
       document.getElementById('detail-server').textContent = cfg.server || '-';
+
+      const updateBanner = document.getElementById('update-banner');
+      if (cfg.update_available) {
+        updateBanner.innerHTML = `
+          <div class="service-item" style="background: var(--warning-bg); border-radius: 8px; padding: 0.75rem; margin-bottom: 0.75rem;">
+            <div class="service-icon" style="background: var(--warning);">⬆️</div>
+            <div>
+              <div class="service-text">Mise à jour disponible</div>
+              <div class="service-detail">Version ${cfg.server_version} disponible. <button class="ghost" style="padding: 0; font-weight: 600;" onclick="startAgentUpdate()">Mettre à jour maintenant</button></div>
+            </div>
+          </div>
+        `;
+      } else {
+        updateBanner.innerHTML = '';
+      }
+    }
+
+    function showUpdateProgress(percent, message) {
+      const banner = document.getElementById('update-banner');
+      banner.innerHTML = `
+        <div class="service-item" style="background: var(--info-bg); border-radius: 8px; padding: 0.75rem; margin-bottom: 0.75rem;">
+          <div class="service-icon" style="background: var(--info);">⬇️</div>
+          <div>
+            <div class="service-text">Mise à jour en cours</div>
+            <div class="service-detail">${escapeHtml(message || '')} (${percent || 0}%)</div>
+          </div>
+        </div>
+      `;
+    }
+
+    async function startAgentUpdate() {
+      showUpdateProgress('10', 'Préparation de la mise à jour...');
+      try {
+        const res = await fetch('/api/update', {method: 'POST'});
+        if (!res.ok) {
+          showUpdateProgress('0', 'Erreur ' + res.status);
+        }
+      } catch (err) {
+        showUpdateProgress('0', escapeHtml(err.message));
+      }
     }
 
     async function saveSettings(event) {
@@ -919,6 +981,7 @@
     function showDashboard() {
       showView('dashboard');
       ws.send(JSON.stringify({action: 'get_status'}));
+      loadSettings();
     }
 
     function controlInstance(instanceId, action) {