V129 - Prepare first, then native BG2 import (no character backups)

SAVE ACCOUNT CHARACTER keeps the proven V125/V128 behavior: BG2 exports to the normal characters folder, then only the exact new CHR/BIO pair is physically moved to characters_<account>.

IMPORT is now deliberately two-step:
1. PREPARE ACCOUNT IMPORT physically stages the logged-in account's CHR/BIO files into BG2's normal characters folder.
2. When preparation is confirmed, press CONTINUE TO IMPORT to return to the normal CHARGEN screen.
3. The same button becomes IMPORT ACCOUNT CHARACTER. Press it again from CHARGEN, and BG2 itself opens its stock native CHARGEN_IMPORT list.

No forced CHARGEN_IMPORT menu push is used. No file movement occurs while BG2's native import list is open. Staged source files remain available until a later safe account action returns them to characters_<account>.

No character backups, duplicate copies, restore history, merge, synchronization, or automatic respawn are performed.
