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/mailer.py

@@ -179,28 +179,46 @@ def envoyer_rapport_spool(nb_envoyes: int, destinataires: list[str], nb_echoues:
 
 
 RETRY_INTERVAL = 300  # 5 minutes
+WATCHDOG_INTERVAL = 60  # 1 minute
+
+
+async def _flush_spools():
+    """Vide les spools email + galerie."""
+    from backend.destinations import traiter_booth_spool, taille_booth_spool
+    loop = asyncio.get_event_loop()
+    total_mail = taille_spool()
+    if total_mail > 0:
+        log.info(f"Spool email: retry ({total_mail} en attente)")
+        nb, dests = await loop.run_in_executor(None, traiter_spool)
+        if nb > 0:
+            echoues = total_mail - nb
+            await loop.run_in_executor(None, envoyer_rapport_spool, nb, dests, echoues)
+    total_booth = taille_booth_spool()
+    if total_booth > 0:
+        log.info(f"Spool galerie: retry ({total_booth} en attente)")
+        await loop.run_in_executor(None, traiter_booth_spool)
 
 
 async def tache_spool_periodique():
-    """Retente emails + galerie en spool toutes les 5 min."""
-    from backend.destinations import traiter_booth_spool, taille_booth_spool
+    """Watchdog connectivite (60s) + retry spool (5 min)."""
+    from backend.wifi import watchdog_tick
+    from backend.destinations import taille_booth_spool
     await asyncio.sleep(15)
+    loop = asyncio.get_event_loop()
+    ticks_depuis_flush = 0
     while True:
-        loop = asyncio.get_event_loop()
-        # Emails
-        total_mail = taille_spool()
-        if total_mail > 0:
-            log.info(f"Spool email: retry ({total_mail} en attente)")
-            nb, dests = await loop.run_in_executor(None, traiter_spool)
-            if nb > 0:
-                echoues = total_mail - nb
-                await loop.run_in_executor(None, envoyer_rapport_spool, nb, dests, echoues)
-        # Galerie booth
-        total_booth = taille_booth_spool()
-        if total_booth > 0:
-            log.info(f"Spool galerie: retry ({total_booth} en attente)")
-            await loop.run_in_executor(None, traiter_booth_spool)
-        await asyncio.sleep(RETRY_INTERVAL)
+        result = await loop.run_in_executor(None, watchdog_tick)
+        if result == "restored":
+            await _flush_spools()
+            ticks_depuis_flush = 0
+        else:
+            ticks_depuis_flush += 1
+            if ticks_depuis_flush >= RETRY_INTERVAL // WATCHDOG_INTERVAL:
+                has_spool = taille_spool() > 0 or taille_booth_spool() > 0
+                if has_spool:
+                    await _flush_spools()
+                ticks_depuis_flush = 0
+        await asyncio.sleep(WATCHDOG_INTERVAL)
 
 
 async def tache_spool_demarrage():