Frame Studio and Frame Home: cross-platform builds

Frame Studio now builds for Windows (x64, x86, ARM64), Linux (x64, x86, ARM64)
and macOS (Apple Silicon, Intel):
- studio/platform.h with Win32 and POSIX implementations (dialogs through
  tinyfiledialogs on Linux/macOS), a GLFW window beside the Win32 one, and a
  platform-neutral frame pacer
- MoltenVK support in the renderer (portability enumeration) and bundled in
  the macOS app
- 32-bit builds: large-address-aware, LZMA packing within a 32-bit address space
- unaligned file reads in the loaders go through loadUnaligned (no UB)
- scripts/build-studio.sh, studio/build_windows.bat [x64|x86|arm64],
  cmake/llvm-mingw.cmake, and a GitHub Actions workflow building every target

Frame Home installs without Studio: frame/install-frame-home.{sh,ps1} and
"Install Frame Home.bat" (packaged as FrameHome-installer.zip).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tools/debugview/debug.vert

@@ -0,0 +1,13 @@
+#version 450
+// Debug views (HslRenderer::setDebugView): any mesh, drawn by its position alone in a flat colour per draw.
+#extension GL_EXT_multiview : require
+layout(location = 0) in vec3 position;
+struct Draw { mat4 clipFromModel[2]; mat4 worldFromModel; vec4 color; };
+layout(std430, set = 0, binding = 0) readonly buffer Draws { Draw d[]; } draws;   // one per draw (firstInstance)
+layout(location = 0) out vec3 vWorld;
+layout(location = 1) flat out vec4 vColor;
+void main() {
+    gl_Position = draws.d[gl_InstanceIndex].clipFromModel[gl_ViewIndex] * vec4(position, 1.0);
+    vWorld = (draws.d[gl_InstanceIndex].worldFromModel * vec4(position, 1.0)).xyz;
+    vColor = draws.d[gl_InstanceIndex].color;
+}