V293 - Native Character Export -> characters/<accountname>

Fixes V292's failure where pressing Export Done could result in no CHR being
created. BG2's original Export Done callback now always executes; neither a
missing router response nor a failed optional file write may cancel it.

After native BG2 creates characters/NAME.CHR (and optional NAME.BIO), the
running account router checks an explicit export authorization, moves the
newly exported files into characters/<logged account>/, and exposes hardlinks
back to BG2's normal Import/Export list. It also updates the account's
character bindings immediately so the new CHR is importable without another
login. No account character files are backed up or automatically copied.

Authorization sources in order:
  - Short direct request file written immediately by Lua when io.open exists
    (e.g. in a compatible EEex installation).
  - Existing native Export INI section.
  - Existing account router command.

The direct request file is a small temporary two-line notification, NOT a
character file or backup, and contains neither a password nor game data.
The router checks account name, filename, session age and modification time
before adopting a character; unrelated loose old files are not imported.

Installation:
  1. Close every BG2 and InfinityLoader instance.
  2. Extract the ZIP into your existing All Editors folder.
  3. Run SETUP_IN_GAME_ACCOUNTS.bat and click INSTALL V293.
  4. Start BG2, log in, and Export using a short filename like TEST01.
  5. Allow a few seconds for the router, then inspect
       Documents/Baldur's Gate II - Enhanced Edition/characters/<accountname>/
     You should find TEST01.CHR there. Reopen native Import to verify it.

Do not manually delete CHR/BIO files while BG2 is running. Your existing
account character folders are preserved. The earlier cleanup of unassigned
root files remains enabled. In-game testing on Windows is still necessary.
If the CHR does not appear, inspect the file root/characters and the account
router log in the Documents profile under _DRAKHYSYS_ACCOUNT_LOGS/<account>/.
