* Support generic ARM64 (Linux, Windows) for Voodoo JIT codegen

The ARM64 Voodoo JIT was already mostly portable — W^X calls were behind
__APPLE__ guards, and the NO_CODEGEN gate already included _M_ARM64.
The only missing piece was a Windows ARM64 I-cache flush path using
FlushInstructionCache instead of GCC/Clang's __clear_cache builtin.


* Add comprehensive testing and technical documentation

- Add TESTING-GUIDE.md: User-facing build/test guide for macOS ARM64
  - Prerequisites, build instructions, VM setup
  - Voodoo configuration (Dynamic Recompiler toggle, JIT debug logging)
  - Testing matrix, what to look for, issue reporting

- Add ARM64-CODEGEN-TECHNICAL.md: Deep technical reference
  - Architecture overview, register allocation, encoding macros
  - Complete pipeline phases walkthrough (prologue through epilogue)
  - Key differences from x86-64, known issues, maintenance guide

- Archive old planning/debug docs to voodoo-arm64-port/archive/
  - Moved 11 working docs to archive (checklist, debug sessions, etc.)
  - Keeps main directory clean with only user-facing documentation


* Remove hardcoded username from VM paths

- Replace /Users/anthony with $HOME in test-with-vm.sh
- Replace /Users/anthony with ~ in archived debugging doc
- Makes repo safe to share publicly without personal info