Map: zoomed-view symbols centred, 10x reveal and enemy range; progress screen on the menu background

- Megamap / TAB map zoomed view: heroes' markers and the other symbols
  (integer 200h centre immediates) follow the view's centre.
- Map reveal: the hero's reveal stamp scaled 10x (mods/mapreveal.cpp,
  docs/map-reveal.md); creatures on the zoomed map shown within 10x the
  sight range.
- Load / save progress screen drawn on the rock background across the full
  width, the picture blended over it (mods/loadingscreen.cpp); the classic
  1024x768 frame is gone.

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

CMakeLists.txt

@@ -74,8 +74,10 @@ add_library(sacredK SHARED
     src/mods/screen.cpp
     src/mods/characters.cpp
     src/mods/mainmenu.cpp
+    src/mods/mapreveal.cpp
     src/mods/questfail.cpp
     src/mods/anticheat.cpp
+    src/mods/loadingscreen.cpp
 )
 target_include_directories(sacredK PRIVATE src)
 target_compile_options(sacredK PRIVATE ${SACREDK_CXX_FLAGS})