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/walktest/edgecheck.cpp

@@ -0,0 +1,38 @@
+// How straight the walkable area's edge runs along a straight wall at an angle: a 20 m floor and a 3 m wall turned by
+// each angle, baked; the edge found every 2 cm along the wall, its wobble off a straight line reported (cm).
+#include "walkgrid.h"
+#include <cmath>
+#include <cstdio>
+int main() {
+    for (float deg : {0.0f, 10.0f, 27.0f, 45.0f, 63.0f}) {
+        HomeWorld w;
+        WorldCollider fl; fl.kind = WorldCollider::Box; fl.role = WorldCollider::Solid; fl.half[0] = 10; fl.half[1] = 0.05f; fl.half[2] = 10; fl.world[13] = -0.05f;
+        WorldCollider wa; wa.kind = WorldCollider::Box; wa.role = WorldCollider::Solid; wa.half[0] = 4; wa.half[1] = 1.5f; wa.half[2] = 0.1f;
+        const float a = deg * 0.0174533f, c = std::cos(a), s = std::sin(a);
+        wa.world[0] = c; wa.world[2] = -s; wa.world[8] = s; wa.world[10] = c; wa.world[12] = 0.37f; wa.world[13] = 1.5f; wa.world[14] = 0.21f;
+        w.colliders = {fl, wa};
+        WorldPoint sp; sp.pos[0] = -3; sp.pos[2] = 3; w.spawns.push_back(sp);
+        std::vector<WalkSource> src;
+        std::vector<std::vector<float>> P;
+        std::vector<std::vector<uint32_t>> I;
+        walkColliderSources(w, src, P, I);
+        WalkParams prm;
+        auto g = buildWalkGrid(src, walkSeeds(w), prm, nullptr);
+        // along the wall (its x axis), the edge's distance from the wall's face on the +z side (towards the spawn side)
+        const float nx = s, nz = c;   // the wall frame's z axis in world
+        std::vector<float> off;
+        for (float t = -3; t <= 3; t += 0.02f) {
+            const float bx = wa.world[12] + c * t, bz = wa.world[14] - s * t;
+            float lo = 0.0f, hi = 0.6f;
+            if (!g->walkable(bx + nx * hi, bz + nz * hi, 0)) continue;
+            for (int k = 0; k < 20; ++k) { const float m = (lo + hi) / 2; (g->walkable(bx + nx * m, bz + nz * m, 0) ? hi : lo) = m; }
+            off.push_back(hi);
+        }
+        double m = 0, v = 0, mn = 1e9, mxv = -1e9;
+        for (float o : off) { m += o; mn = std::min<double>(mn, o); mxv = std::max<double>(mxv, o); }
+        m /= std::max<size_t>(1, off.size());
+        for (float o : off) v += (o - m) * (o - m);
+        std::printf("wall at %4.0f deg: edge %.1f cm off its face, wobble %.2f cm rms, %.2f cm peak to peak (%zu samples)\n", deg, (m - 0.1) * 100,
+                    std::sqrt(v / std::max<size_t>(1, off.size())) * 100, (mxv - mn) * 100, off.size());
+    }
+}