Add macOS support

[VjiaoBlack]

Summary

• Adds macOS (OpenGL 4.1 / Metal) compatibility while preserving the existing Linux fast path
• All OpenGL 4.3/4.4 code is kept behind #ifndef TINYENGINE_OS_MAC guards — Linux builds are unchanged
• Shaders downgraded from GLSL 430 to 410, which is a compatible subset (no behavioral change on 4.3+ drivers)

Changes

• Makefile: detects Darwin via uname, sets clang++, -framework OpenGL, homebrew paths, -DTINYENGINE_OS_MAC
• source/vertexpool.h: #ifdef TINYENGINE_OS_MAC fallbacks for:
  • glVertexAttribPointer instead of glVertexAttribFormat / glBindVertexBuffer (GL 4.3)
  • glBufferData + CPU buffer instead of glBufferStorage + persistent mapping (GL 4.4)
  • glDrawElementsBaseVertex loop instead of glMultiDrawElementsIndirect (GL 4.3)
• Shaders: #version 430 core → #version 410 core, removed const on local vars (Apple GLSL rejects this)
• SimpleHydrology.cpp: fixed UB in version assert (strcmp instead of == on char[])

Prerequisites

TinyEngine must also be compiled with -DTINYENGINE_OS_MAC on macOS (its Makefile examples already do this).

Test plan

• Verify Linux build is unchanged (no TINYENGINE_OS_MAC defined → original GL 4.3 path)
• Verify macOS build compiles and runs with make all
• Verify simulation runs correctly on macOS (press P to unpause)

🤖 Generated with Claude Code

[VjiaoBlack]

tested on Mac!