Add native macOS (Apple Silicon) support - #102

…JIT-fix approach

Replace the custom-allocator + module-bisecting workaround stack with the
upstream macOS approach from PathOfBuildingCommunity/PathOfBuilding-SimpleGraphic
PR PathOfBuildingCommunity#102, which fixes the arm64/GC64 allocation problem at the source by
pinning a patched LuaJIT (port 2026-03-30_1, ref 18b087cd) rather than
working around it in the engine.

Removed (no longer needed once LuaJIT is fixed correctly):
- mac_gc64_alloc custom allocator + magic sentinel (ui_main.cpp)
- mac_pload_* / bisect / coroutine module-loading machinery (~1050 lines
  across ui_api.cpp and ui_main.cpp) that worked around Data.lua load
  failures, themselves a symptom of the same GC64 bug
- sys_IMain::launchCwd and the host argv handling in sys_main.cpp
- mac/entry.cpp (win/entry.cpp already compiles on macOS via its
  visibility macros and _WIN32 guards, matching upstream)

Adopted from PR PathOfBuildingCommunity#102:
- Patched LuaJIT vcpkg port (2026-03-30_1) + arm64-osx triplet + version
  files; baseline bumped to 2026-05-22
- AppendLocalLuaSubdir() replacing inline package.path logic
- Retina/HiDPI cursor scaling + GLFW_ANGLE_PLATFORM_TYPE_METAL (sys_video.cpp)
- .app bundle base-path detection (sys_main.cpp)
- Portable std::this_thread::sleep_for and size_t casts (r_main/r_texture)
- VirtualScreenHeight() in r_font; base64/common include + guard fixes
- Lua-cURLv3 luaL_setfuncs patch + CMake patch-application; WIN32-guarded
  lua-utf8/luasocket; ZSTD target selection

Retained (our only divergence, additive and APPLE-guarded):
- pob-host launcher executable (mac/host.cpp -> "Path of Building-PoE2")
  that links the dylib for a runnable dev binary; upstream defers this to
  a separate launcher repo. The host shifts argv itself so the engine
  stays identical to upstream.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E69xvgJuYgUaR1eHY3Qf3o

…ildingCommunity#102

Two fixes from nelkonandparker's macOS port (PathOfBuildingCommunity#102) that this branch
lacked:
- Scale cursor coordinates by the framebuffer/window-size ratio so
  clicks and tooltips align on HiDPI (Retina) displays; the ratio is
  1.0 on Windows, leaving its behavior unchanged.
- Explicitly select ANGLE's Metal backend on macOS (GLFW init hint,
  APPLE-guarded) and request the port's metal feature for osx in the
  vcpkg manifest.

Co-authored-by: nelkonandparker <nelkonandparker@users.noreply.github.com>