V287 — V271 login behavior + automatic cleaning of the shared characters root

BASE: V271, not V286. V271 account/login logic, native Import/Export UI and
characters/<accountname> permanent storage are retained.

Changes:
- The V271 router deletes *loose* .CHR and .BIO files immediately inside the
  Documents BG2 profile's characters/ root when no account is active.
- The cleanup repeats approximately every 0.1 seconds while the router is
  running and the account view is inactive.
- Before a new account's first character-folder mount, leftover root .CHR/.BIO
  files are removed; so old orphans no longer block login.
- DURING an active account session: temporary file aliases and native new
  exports in characters/ must NOT be deleted, and native stock Import/Export
  continues to work. The router finalizes exports in characters/<accountname>.
- The hidden account-deletion router command remains disabled (as the UI is).
- Cleanup never descends into characters/<accountname> or modifies .JSON,
  settings, account flags, etc.

WARNING: root .CHR/.BIO deletion is permanent, with NO character backups.
Any character you want to keep must be moved into characters/<accountname>
BEFORE installing. Close ALL BG2 and InfinityLoader instances before setup.

HOW TO INSTALL
1. Close BG2, all BG2 windows, InfinityLoader and the old account router.
2. Extract V287 to your editor workspace.
3. Run SETUP_IN_GAME_ACCOUNTS.bat and choose your BG2 game folder and the
   Documents/Baldur's Gate II - Enhanced Edition folder containing Baldur.lua.
4. Click INSTALL V287 and start BG2 normally.

LIMITATION: V271 maintains one shared native characters root per BG2 Documents
profile. Separate simultaneously running games require isolated profiles.
An external program that reinserts files while a native account session is
active cannot be distinguished from BG2 exporting a new file without changing
BG2's native Export behavior; cleanup pauses during that period.

No in-game test was possible here. Use a test account before important play.
