scheduler: process newest UIDs first to prioritize fresh mail

The per-rule batch was sliced from all_uids in server order (oldest
UID first), so with a big backlog the scheduler chewed through years
of unmatched newsletters before reaching the current invoices the
user was actually waiting on. Sort new_uids descending by int (with a
plain reverse() fallback for non-numeric UIDs) so each poll picks the
newest 500 first. Old backlog still gets worked off in the background.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/services/scheduler.py

@@ -115,7 +115,15 @@ def _poll_account_sync(account_id: int) -> None:
                     .all()
                 )
 
+                # Neueste UIDs zuerst — sonst arbeitet der Scheduler bei großem
+                # Backlog erst durch Jahre alte Newsletter, bevor er aktuelle
+                # Rechnungen erreicht. UIDs sind auf IMAP-Servern monoton
+                # steigend, daher sortiert reverse-int zuverlässig neu→alt.
                 new_uids = [uid for uid in all_uids if uid not in processed_uids]
+                try:
+                    new_uids.sort(key=int, reverse=True)
+                except (ValueError, TypeError):
+                    new_uids.reverse()
 
                 if not new_uids:
                     write_log(