V271 - NORMAL BG2 IMPORT / EXPORT INTO characters/<accountname>

Example profile (Documents/Baldur's Gate II - Enhanced Edition):
  characters/
    Drakhysys/   <-- characters exported by account Drakhysys
    Kronas/      <-- characters exported by account Kronas

HOW TO INSTALL
  1. Close all BG2 windows and any existing router/helper processes.
  2. Extract All Editors to your editor workspace.
  3. Run SETUP_IN_GAME_ACCOUNTS.bat and select BG2 folders as before.
  4. If using old accounts, MANUALLY move each old folder
     characters_Drakhysys -> characters/Drakhysys, etc.
     Keep _DRAKHYSYS_ACCOUNT_FLAG.json in the moved directory.
  5. Old CHR/BIO files directly in characters/ must be moved manually
     into the desired nested account folder BEFORE logging in.

WHAT CHANGED
  * Account creation creates characters/<accountname>.
  * Account names retain original case; case-only duplicates are not accounts.
  * BG2 original Import Character and Export Character panels are preserved.
  * Only logged-in account files are visible in native character UI.
  * Actual CHR/BIO files remain in the account directory.
  * Windows NTFS hardlinks provide temporary aliases in characters/ while
    logged in. New native exports are finalized into the account directory.
  * No automatic backups or restoration, no migration or deletion of old files.
  * Account deletion in UI remains disabled from the starting v268 baseline.

Technical limitation: All accounts sharing the same BG2 Documents profile
should not log in at the same time. This implementation uses one active
`characters/` root view, just as BG2's native character UI does.
Filesystem unit tests passed on the development host; in-game behavior must
be tested on Windows and NTFS before relying on it with important characters.
