V159 - ACCOUNT FOLDER MIRROR + NORMAL BG2 IMPORT / EXPORT - NO BACKUPS

Behavior:
1. LOGIN / ACCOUNT FOLDER CHECK
   - Each account owns characters_<accountname>.
   - Successful login connects BG2's literal characters path directly to that matching account folder.
   - The account screen reports READY only after the mirror is confirmed.

2. NORMAL IMPORT
   - The stock BG2 Import action is kept: createCharScreen:OnImportCharacterButtonClick().
   - The stock CHARGEN_IMPORT screen is kept.
   - Because characters already mirrors the logged-in account folder, only that account's CHR/BIO files are visible.

3. NORMAL EXPORT
   - The stock BG2 Export action is kept: characterScreen:OnExportButtonClick().
   - The stock CHARACTER_EXPORT and CHARGEN_EXPORT screens are kept.
   - Selecting an existing filename and pressing Done uses BG2's normal overwrite confirmation.
   - The write goes directly through characters into characters_<accountname>.

4. NO AUTOMATIC CHARACTER BACKUPS
   - No CHR/BIO copy backup is created.
   - No deleted character is recreated on logout, restart, import, export, or account switching.
   - Switching accounts only reconnects the characters junction to the newly logged-in account folder.

Install with SETUP_IN_GAME_ACCOUNTS.bat.

V159 availability correction:
- Import uses BG2 stock clickable condition only: current screen is CHARGEN.
- Export uses BG2 stock characterScreen:IsExportButtonClickable() only.
- Neither native button depends on drakRouteReady(), so a delayed/stale route reply cannot gray the button.
- Login still creates the characters -> characters_<account> junction; no CHR/BIO backup/copy behavior was added.
