ci: fix bonsai cross-platform build on Linux, macOS arm64, Windows x64

Bundles four portability fixes uncovered by manually firing the platform
workflows against this branch:

- WgpuOverlayRenderer.cpp: GCC 11 (Rocky manylinux runner) does not parse
  a multi-line raw string inside `#define`. Converted
  THICK_LINE_HELPERS_WGSL from a `#define` to a `static const char*` and
  switched AXIS_WGSL / SECTION_WGSL / MARQUEE_WGSL to `std::string` so
  they can concatenate at static-init time. Three call sites now pass
  `.c_str()` to svFromCStr.

- bonsaiviewer/CMakeLists.txt: added BUNDLE DESTINATION to the install
  rule (same fix already applied to IfcViewerWgpuMinimal). MACOSX_BUNDLE
  targets fail at configure on macOS without it even when nobody runs
  `make install`.

- build_osx.yml: dropped the x64 (Intel cross-compile) matrix row. The
  runner is arm64 so `brew --prefix qt` returns the arm64 prefix; we'd
  need a separate x86_64 Qt install under /usr/local to cross-build
  BonsaiViewer. Revisit if Intel-Mac demand resurfaces.

- build_win.yml: dropped the ARM64 matrix row. wgpu-native does not ship
  a Windows-ARM64 binary, so IfcViewerWgpu's link step fails with ~60
  unresolved wgpu* externs. Re-enable when upstream publishes that
  target.

Cherry-pick this commit to v0.8.0 so the workflow_dispatch buttons see
the dropped rows.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.github/workflows/build_osx.yml

@@ -10,10 +10,11 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: macos
-            runner: macos-14
-            arch: x64
-            oldarch: 
+          # x64 (Intel cross-compile) dropped while wgpu Qt is required:
+          # the runner is arm64 so `brew --prefix qt` returns the arm64
+          # prefix; we'd need a separate x86_64 Qt install under
+          # /usr/local to cross-build BonsaiViewer. Revisit if Intel-Mac
+          # demand resurfaces.
           - os: macos
             runner: macos-14
             arch: arm64

.github/workflows/build_win.yml

@@ -16,12 +16,11 @@ jobs:
             build_branch: windows-x64
             zip_suffix: win64
 
-          - arch: ARM64
-            runs_on: windows-11-arm
-            deps_dir: _deps-vs2022-ARM64-installed
-            vcvars: '"C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Auxiliary\Build\vcvarsarm64.bat"'
-            build_branch: windows-arm64
-            zip_suffix: win-arm64
+          # ARM64 dropped while BonsaiViewer is on: wgpu-native does not
+          # ship a Windows-ARM64 binary, so IfcViewerWgpu's link step fails
+          # with ~60 unresolved wgpu* externs. Re-enable when upstream
+          # publishes that target (or when we add ARM64 to the wgpu-native
+          # FetchContent URL allowlist).
 
     runs-on: ${{ matrix.runs_on }}