Add sackit integration and improve build system

[Santiagocetran]

Overview

Sorry for the sloppy vibecoded shit i believe this is a friendlyer PR :) Ive fixed the Cmake and added sackit as submodule for easyer startup setup. Hope you can at least take a quick look and give me feedback, im learning.

This PR adds sackit integration to iceball and improves the build system with modern CMake practices.

Changes

Core Integration

• Sackit submodule: Added .gitmodules and external/sackit submodule
• CMake support: Updated CMakeLists.txt with proper sackit detection and linking
• Makefile updates: Updated all Makefiles (main, mingw, osx) for sackit linking

Build System Improvements

• Enhanced CMake: Improved Lua/LuaJIT detection with better error handling
• Better .gitignore: Comprehensive rules to prevent build artifact inclusion
• CMake config: Added proper CMake configuration template

Documentation

• README.md: Updated with sackit information and setup instructions
• BUILD_ANALYSIS.md: Comprehensive build system analysis and improvements
• docs/Instructions.md: New detailed setup and build instructions

Key Features

• ✅ Clean integration without build artifacts
• ✅ Cross-platform support (Linux, Windows, macOS)
• ✅ Proper CMake submodule handling
• ✅ Enhanced build system reliability
• ✅ Comprehensive documentation

Testing

• Builds successfully on Linux with CMake and Make
• Sackit submodule initializes correctly
• All existing functionality preserved

Notes

This is a clean version that addresses previous feedback about including build artifacts. Only essential source code and configuration changes are included.