Two related fixes for abandoned pairings:
- After /pair starts a Baileys session, arm a 5-minute timer. If the
operator doesn't scan in time the bot stops the session, deletes the
pending account row + session files, and pings them in Telegram.
- On bot startup, sweep any 'pending' account rows older than 1 hour —
catches the case where the bot was restarted mid-pair, leaving a
stale row no in-memory state could clean up.
