Prepare native UI shaders before Linux SDK-container client builds

Normal Linux run-client-dev.sh now references PRK.Fonts.Vulkan/PRK.Gui.Vulkan, whose embedded shaders are compiled by MSBuild. The plain mcr.microsoft.com/dotnet/sdk:10.0 container has no glslc, so a fresh/stale-output build fails with MSB3073 exit 127. Playground run.sh already compiles the same four shaders on the host before its SDK build. User explicitly requested no more scripts. Keep the existing playground implementation unchanged and add the same four host glslc invocations directly to run-client-dev.sh; preserve native compiler defaults/overrides for ordinary SDK/CI/platform builds. Verified exact failure from a clean archived source tree in plain mcr.microsoft.com/dotnet/sdk:10.0: MSB3073 because glslc is absent. Removed all four generated SPIR-V files and ran actual ./run-client-dev.sh --build-only after the inline fix; host prepared all four, the plain container build passed with zero warnings/errors, and outputs exist. bash -n and git diff --check pass. Added clear host glslc prerequisite check alongside Docker. No new helper script remains. User explicitly requested using /home/mathias/Projects/engines directly, no worktree. Branch fix/prepare-native-ui-shaders; generated Avalonia directories remain untouched. No commit/push or Windows VM requested.