V192 — V176 CHARACTERS + PER-ACCOUNT ACTIVATE + DEACTIVATE ON LOGOUT/QUIT

- Base character Import/Export behavior remains V176 and is checksum-tested unchanged.
- Each account keeps its own independent <ACCOUNTNAME> Activate flag.
- Login sets only that account flag to 1.
- LOG OUT sets only the leaving account flag to 0.
- Quit to Main Menu sets only the leaving account flag to 0 before BG2 changes screen.
- Full BG2 shutdown / quit prompt sets only the leaving account flag to 0 before shutdown.
- Setup clears stale Activate=1 flags left by V191 while BG2 is closed.
- Account/password records and characters are not altered by stale-flag cleanup.
- No automatic character backup or restore behavior.
