Five new VCKExpansion classes plus integration glue:
- ShaderLoader      loads SPIR-V (.spv) and optional GLSL via glslangValidator
- ShaderWatcher     polls .spv timestamps for hot reload
- SpecConstants     VkSpecializationInfo builder
- ShaderStage       per-stage VertexLayout / PushConstants / binding decls
- ShaderInterface   merges ShaderStages into pipeline cfg + descriptor layouts
- ApplyToConfig     convenience helper

PushConstants gains Declare(name, type, count) array overload + SetRaw.
VulkanPipeline::Config gains vertSpecialization / fragSpecialization
plumbed into pSpecializationInfo for both shader stages.

VCK.h class index extended to 20 expansion classes ([26]-[30]).

PR #10 (code) + PR #11 (changelog + version bump). CI green on
Linux + macOS + Windows MinGW + Windows MSVC at both merges.