fix: defer expiry reminders for trial and bonus subscriptions

Trial and registration/referral-bonus subscriptions usually last only a
few days, so the multi-day ending-soon reminders fired almost the moment
they were granted and needlessly alarmed newcomers.

Track this with a new subscription flag (suppress_early_expiry_notifications,
migration 0035): trial activation, referral welcome bonus and inviter bonus
grants set it, while a real paid purchase clears it on upsert. While set, the
notification worker skips the day-before stages but still sends the
hours-before reminder and the expiry/after-expiry notices, so users are
warned shortly before access ends. Once they pay for a full subscription the
complete reminder spectrum resumes.

backend/bot/services/referral_service.py

@@ -197,6 +197,9 @@ class ReferralService:
                                     "status_from_panel": "ACTIVE_BONUS",
                                     "traffic_limit_bytes": self.settings.user_traffic_limit_bytes,
                                     "auto_renew_enabled": False,
+                                    # Short bonus grant: warn only hours before it
+                                    # ends, not days ahead. A real payment clears this.
+                                    "suppress_early_expiry_notifications": True,
                                 }
                                 try:
                                     await subscription_dal.deactivate_other_active_subscriptions(