Package viewer shaders and harden LUS startup

[mckinlee]

Summary

• package the pinned libultraship shader set as a reproducible sidecar archive
• preflight viewer assets and report startup failures cleanly
• shut down ImGui backends while the pinned renderer and context are still alive
• place the sidecar beside Torch in hosted artifacts and custom runtime layouts

Testing

• MSVC x64 Release builds with BUILD_UI=ON and BUILD_UI=OFF
• fresh UI build with a custom CMAKE_RUNTIME_OUTPUT_DIRECTORY
• deterministic three-entry shader archive generation and inventory check
• missing, corrupt, versioned-incomplete, and default-launch missing-sidecar failures
• source-free DirectX viewer open, three-second hold, close, and exit 0 from default and custom runtime layouts
• clang-format 14 dry run, workflow YAML parsing, Python syntax, and git diff --check