Resilience : ecran pause, reconnexion WS auto, watchdog systemd, WiFi monitor

- WebSocket : reconnexion avec backoff exponentiel au lieu de reload page
- Ecran pause avec tasse de cafe quand le backend est injoignable
- Endpoint /api/health pour monitoring externe
- Watchdog systemd (sd_notify READY=1 + WATCHDOG=1 toutes les 10s)
- Service systemd durci (Type=notify, WatchdogSec=30, KillMode, limites)
- WiFi watchdog : script + timer systemd, verifie la gateway toutes les 60s
- Destinations : fallback url_tunnel (WireGuard) en priorite

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

frontend/js/websocket.js

@@ -1,30 +1,38 @@
-/* Communication WebSocket avec le backend */
+/* Communication WebSocket avec le backend — reconnexion résiliente */
 
 let ws = null;
-let wsReconnectTimer = null;
+let _wsReconnectDelay = 1000;
+let _wsWasConnected = false;
 const wsCallbacks = {};
 
 function wsConnecter() {
   const proto = location.protocol === 'https:' ? 'wss:' : 'ws:';
-  ws = new WebSocket(`${proto}//${location.host}/ws`);
+  try { ws = new WebSocket(`${proto}//${location.host}/ws`); } catch(e) { _wsScheduleReconnect(); return; }
 
   ws.onopen = () => {
     console.log('WebSocket connecte');
-    if (wsReconnectTimer) {
-      clearInterval(wsReconnectTimer);
-      wsReconnectTimer = null;
+    _wsReconnectDelay = 1000;
+    if (_wsWasConnected) {
+      _masquerPause();
+      // Recharger la config pour resynchroniser l'état
+      if (typeof chargerConfig === 'function') chargerConfig();
     }
+    _wsWasConnected = true;
   };
 
   ws.onmessage = (event) => {
-    const msg = JSON.parse(event.data);
-    const cbs = wsCallbacks[msg.type];
-    if (cbs) cbs.forEach(cb => cb(msg));
+    try {
+      const msg = JSON.parse(event.data);
+      const cbs = wsCallbacks[msg.type];
+      if (cbs) cbs.forEach(cb => cb(msg));
+    } catch(e) {}
   };
 
   ws.onclose = () => {
-    console.log('WebSocket deconnecte, rechargement dans 5s...');
-    setTimeout(() => { location.reload(); }, 5000);
+    console.log('WebSocket deconnecte');
+    ws = null;
+    _afficherPause();
+    _wsScheduleReconnect();
   };
 
   ws.onerror = () => {
@@ -32,6 +40,26 @@ function wsConnecter() {
   };
 }
 
+function _wsScheduleReconnect() {
+  const delay = Math.min(_wsReconnectDelay, 10000);
+  _wsReconnectDelay = Math.min(_wsReconnectDelay * 1.5, 10000);
+  setTimeout(wsConnecter, delay);
+}
+
+function _afficherPause() {
+  const el = document.getElementById('ecran-pause');
+  if (el) el.style.display = 'flex';
+}
+
+function _masquerPause() {
+  const el = document.getElementById('ecran-pause');
+  if (el) { el.style.display = 'none'; }
+  // Relancer le preview si on était sur l'accueil
+  if (typeof lancerPreview === 'function' && document.getElementById('ecran-accueil')?.classList.contains('actif')) {
+    lancerPreview();
+  }
+}
+
 function wsEnvoyer(msg) {
   if (ws && ws.readyState === WebSocket.OPEN) {
     ws.send(JSON.stringify(msg));