Skill hotkeys cast the skill; skills on 1-5, weapon sets on 6-0

A digit that selects a combat-art slot now also presses the right mouse
button (posted WM_RBUTTONDOWN, released with the key), so the game casts
the art at the cursor like a right-click. SwapDigits trades the digit
rows; the key rewrite shares the WASD remap in the engine/UI receivers.

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

CMakeLists.txt

@@ -34,6 +34,7 @@ add_library(sacred_re SHARED
     src/mods/widescreen.cpp
     src/mods/hud.cpp
     src/mods/wasd.cpp
+    src/mods/skillkeys.cpp
 )
 target_include_directories(sacred_re PRIVATE src)
 target_compile_options(sacred_re PRIVATE ${SACRED_RE_CXX_FLAGS})