fix: push delivery when app is closed

- TTL 30s -> 86400 (24h): push services were dropping undelivered notifs
- Urgency: high: wakes device from doze/sleep
- Topic: per-user to collapse duplicate pending pushes
- SW push handler: try/catch for malformed payloads, always call waitUntil
- Bump SW cache to v6

internal/push/handlers.go

@@ -167,7 +167,9 @@ func (h *Handler) SendPush(ctx context.Context, userID string, payload map[strin
 			Subscriber:      h.vapidSubj,
 			VAPIDPublicKey:  h.vapidPub,
 			VAPIDPrivateKey: h.vapidPriv,
-			TTL:             30,
+			TTL:             86400,
+			Urgency:         webpush.UrgencyHigh,
+			Topic:           userID,
 		})
 		if err != nil {
 			h.logger.Error("failed to send push", "error", err, "user_id", userID)
@@ -242,7 +244,9 @@ func (h *Handler) SendChannelNotification(ctx context.Context, channelID, author
 			Subscriber:      h.vapidSubj,
 			VAPIDPublicKey:  h.vapidPub,
 			VAPIDPrivateKey: h.vapidPriv,
-			TTL:             30,
+			TTL:             86400,
+			Urgency:         webpush.UrgencyHigh,
+			Topic:           userID,
 		})
 		if err != nil {
 			h.logger.Error("failed to send push", "error", err, "user_id", userID)