V289 - V288 base: native BG2 LAN campaign join + Character File-only import

- Account creation/login remains V271-derived from V287/V288.
- Per-account settings/backups and characters/<accountname> are preserved.
- Shared root CHR/BIO cleanup from V287 remains active. Files outside account
  directories can be deleted WITHOUT backup when no account is mounted.
- CHARGEN Import now invokes OnImportCharacterFileButtonClick(), skipping
  the Saved Game import choice. Native list, selection and Done/Cancel remain.
- Use Multiplayer -> CONNECTION -> JOIN CAMPAIGN, and choose:
   SHADOWS OF AMN (SoA)  => bg2ee-main
   THRONE OF BHAAL (ToB) => bg2ee-tob
   THE BLACK PITS II (TBP II) => bg2ee-bp
- Native LAN discovery is used, not sequential local IP address guesses.
- One available host for the selected campaign -> native LAN join.
- Password-protected host -> native password entry before joining.
- Multiple available hosts -> filtered native session list for manual choice.
- No available host in the current discovered list -> native Create Game for
  chosen campaign, named SoA-1 / ToB-1 / TBP-1, etc.
- Full (6-player) parties aren't joinable; Create Game uses next number
  after highest discovered session name for that campaign.
- Join becomes the native multiplayer arbitration screen AFTER BG2 connects;
  the update does not falsely open arbitration before joining.
- Same host computer, same normal BG2 multiplayer session. It does not
  spawn additional BG2 instances, hosts or IP bindings.

IMPORTANT:
LAN discovery is asynchronous. If the list is stale, use REFRESH HOSTS and
wait before choosing your campaign. An empty list is not proof that there are
no currently running hosts; Windows Firewall and LAN setup can block discovery.

INSTALL:
Close BG2. Extract archive and run SETUP_IN_GAME_ACCOUNTS.bat. Choose BG2
installation and Documents folder containing Baldur.lua. INSTALL V289.

No automatic character backups; live BG2/Windows multiplayer test required.
