Bundle and verify the Vulkan loader in Windows releases

[ppXD]

Summary

• stage LunarG's official checksum-pinned x64 Vulkan loader and runtime license
• merge the Vulkan resources into GPU release installers
• verify Sherpa/ONNX/Vulkan runtime payloads by extracting NSIS packages
• smoke-launch the packaged Windows executable for 15 seconds
• run the real Vulkan installer workflow on relevant pull requests

Why

The v0.4.0 Windows binary directly imports vulkan-1.dll, but the draft installer did not include it. Machines without a Vulkan-capable display driver therefore could fail before Wisp could reach its advertised CPU fallback.

Local verification

• official Vulkan runtime archive SHA-256 verified
• staged loader is a PE32+ x86-64 DLL
• old v0.4.0 installer correctly fails the new --require-vulkan gate
• synthetic complete runtime directory passes the gate
• workflow YAML, JSON configs, shell syntax, rustfmt, and diff checks pass

The PR CI runs the real Windows Vulkan installer build, extraction checks, and packaged-app launch smoke.