Characters: campaigns, "Spielen" main menu, story unlocks

- One world per campaign and difficulty in a character file (sections
  ancaria<d> / underworld<d>; old world<d> renamed when read). Difficulty
  unlocks by the shared hero's story completions (hero header +0xed..),
  shared by both campaigns.
- Main menu: "Kampagne Ancaria", "Kampagne Underworld" and "Spielstaende"
  become "Spielen" (mods/mainmenu.cpp). The load window lists all
  characters, the world dialog offers both campaigns, "Neuer Charakter"
  asks for the campaign and opens character creation.
- Character window: no Underworld import mode (new Underworld heroes, all
  classes, slots light up), no "Importieren"; load window without
  "Speichern".

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tools/names.txt

@@ -344,3 +344,7 @@
 0x006bb870 cUI_EscMenu::BuildLines            # line actions; "Spielstaende" text 0x41b at 0x6bc1f7
 0x00810af0 BringWindowToFront                 # (hwnd, timeout), ret 8; loops forever with timeout -1
 0x0072ad60 cUI_Button2::SetCaption            # (text id, font), ret 8 -> +0xa4 / +0xa0
+0x00712f30 cUI_MainMenu::BuildEntries     # thiscall, plain ret: the menu entries (cUI_StaticText64FX); main page vector +0x158
+0x00711fa0 cUI_MainMenu::HandleEvent      # vf10: sets g_campaign 0x182cdc8 by entry name (NEWGAME 0, NEWADDON 1)
+0x00753d70 cUI_StaticText64FX::cUI_StaticText64FX  # (name, rect, parent, ?, text id, command, flags)
+0x0070e2a0 cUI_Character::Show               # vf24 (shown), ret 4: single player + g_campaign 1 -> mode 7 (Underworld import, level 25+)