macOS support (Apple Silicon + Intel)

[paranoidminotaur]

macOS support (Apple Silicon + Intel)

The game previously built on macOS but rendered a black window via the broken GLUT
backend, had no keyboard or gamepad input, and had no audio. This PR fixes all of
that and cleans up a few rough edges along the way.

Tested on macOS 15 (Sequoia) with Apple Silicon (M3). The CMake changes should work
on Intel Macs without modification.

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What was broken and why

Rendering — olcPixelGameEngine auto-selected the GLUT backend on macOS.
Modern macOS deprecates GLUT and glutGet(GLUT_SCREEN_WIDTH) returns 0, which caused
the engine to exit immediately. Even when patched past that, the GLUT window rendered
nothing.

Keyboard/gamepad input — The project linked sdl12-compat (an SDL 1.2 shim on top
of SDL2) for joystick support. On macOS, both libSDL-1.2 and libSDL2 export
identical symbol names and share one event queue. sdl12-compat registers a block of
custom SDL2 event type IDs at startup and re-injects all incoming events under those
IDs, so the rendering backend's SDL_PollEvent loop never saw standard SDL_KEYDOWN
or SDL_MOUSEMOTION events — only opaque custom-type events it didn't know about.

Audio — SoundPlayer (the first member constructed in NestrisX86) called
Mix_OpenAudio before SDL_Init had been called by anything else. On some
configurations this silently failed.

CMake — Homebrew paths were hardcoded to /opt/homebrew, which is the Apple
Silicon prefix. Intel Macs use /usr/local.

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Changes

CMakeLists.txt

• Replaced hardcoded /opt/homebrew paths with find_package(SDL2),
  find_package(SDL2_mixer), and find_package(yaml-cpp), which work on both Intel
  and Apple Silicon via their installed CMake config files.
• Removed sdl12-compat (libSDL-1.2) from the macOS and Linux link entirely.
• Updated Linux apt dependencies in comments (libsdl2-dev replaces libsdl1.2-dev).

Build instructions are now:

# macOS
brew install libpng sdl2 sdl2_mixer yaml-cpp

# Linux
sudo apt install libpng-dev libsdl2-dev libsdl2-mixer-dev libyaml-cpp-dev libgl-dev

mkdir build && cd build
cmake .. -DCMAKE_BUILD_TYPE=Release
make -j$(nproc)
./nestris_x86   # run from project root