Normalize executable names and combo box scrolling

[DiyunZ]

• Rename executables to lassie.exe and cmod.exe.
• Update packaging, portable-build scripts, registry entries, and documentation.
• Prevent mouse-wheel scrolling from accidentally changing Lassie combo-box selections while preserving page scrolling.
• Rename piece-experimental.cpp to Piece-experimental.cpp.
• Remove the obsolete, comments-only Piece.cpp; retain the active Piece.h and implementation.