Watchdog WiFi + reconnexion auto + fix timing surprise capture

- Watchdog connectivite toutes les 60s (check TCP 1.1.1.1:53)
- Si offline : scan WiFi et reconnexion auto aux reseaux enregistres
- Si internet restaure : flush immediat des spools (email + galerie)
- Surprise : capture declenchee 500ms apres affichage (au lieu de 1.7s apres)
  pour capturer la reaction naturelle des gens

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

backend/wifi.py

@@ -201,3 +201,62 @@ def wifi_forget(ssid: str) -> dict:
 
 def wifi_get_password(ssid: str) -> str | None:
     return _charger_mdp().get(ssid)
+
+
+# --- Watchdog connectivité ---
+
+_internet_ok = False
+
+
+def check_internet(timeout: int = 5) -> bool:
+    """Teste la connectivité internet (DNS + HTTP rapide)."""
+    import socket
+    try:
+        socket.create_connection(("1.1.1.1", 53), timeout=timeout).close()
+        return True
+    except OSError:
+        return False
+
+
+def watchdog_tick() -> str | None:
+    """Vérifie internet. Retourne 'restored' si passage offline→online, None sinon."""
+    global _internet_ok
+    now_ok = check_internet()
+    if now_ok and not _internet_ok:
+        _internet_ok = True
+        log.info("Internet restauré — flush spool")
+        return "restored"
+    _internet_ok = now_ok
+    if not now_ok:
+        _tenter_reconnexion_wifi()
+    return None
+
+
+def _tenter_reconnexion_wifi():
+    """Si déconnecté du WiFi, tente de se reconnecter à un réseau enregistré visible."""
+    status = wifi_status()
+    if status["connecte"]:
+        return
+    log.info("Pas de WiFi — scan des réseaux enregistrés")
+    saved = {n["ssid"] for n in wifi_saved_list()}
+    if not saved:
+        return
+    try:
+        r = subprocess.run(
+            ["nmcli", "-t", "-f", "SSID,SIGNAL", "dev", "wifi", "list", "--rescan", "yes"],
+            capture_output=True, text=True, timeout=15,
+        )
+        candidates = []
+        for line in r.stdout.strip().split("\n"):
+            p = _nmcli_split(line)
+            if len(p) >= 2 and p[0] in saved and p[1].isdigit():
+                candidates.append((p[0], int(p[1])))
+        candidates.sort(key=lambda x: -x[1])
+        for ssid, sig in candidates:
+            log.info(f"Tentative reconnexion WiFi: {ssid} (signal {sig}%)")
+            result = wifi_connect(ssid)
+            if result.get("succes"):
+                log.info(f"Reconnecté à {ssid}")
+                return
+    except Exception as e:
+        log.warning(f"Reconnexion WiFi échouée: {e}")