fix: move light data from UBO to push constants — fixes std140 layout issue

Root cause: GLSL std140 layout adds padding after mat4 for vec4 fields,
causing light data to be read at wrong offsets → NaN/artifacts.

Fix:
- UBO back to 64 bytes (mat4 vp only)
- Light data (pos + color, 32 bytes) sent via push constants at offset 64
- Two push constant ranges: Vertex (0-64, model) + Fragment (64-96, light)
- Both vertex and fragment shaders read from same push_constant block
- PBR shader fully restored with Cook-Torrance BRDF
- Dynamic point light follows physics ball

src/Engine.Graphics.Vulkan/VulkanPipeline.cs

@@ -150,12 +150,19 @@ internal sealed unsafe class VulkanPipeline : IDisposable
                 pDynamicStates = dynamicStates,
             };
 
-            var pushConstantRange = new VkPushConstantRange
+            var pushConstantRanges = stackalloc VkPushConstantRange[2];
+            pushConstantRanges[0] = new VkPushConstantRange
             {
-            stageFlags = VkShaderStageFlags.Vertex | VkShaderStageFlags.Fragment,
+                stageFlags = VkShaderStageFlags.Vertex,
                 offset = 0,
                 size = 64,
             };
+            pushConstantRanges[1] = new VkPushConstantRange
+            {
+                stageFlags = VkShaderStageFlags.Fragment,
+                offset = 64,
+                size = 32,
+            };
 
             var descLayout = DescriptorSetLayout;
             var layoutInfo = new VkPipelineLayoutCreateInfo
@@ -163,8 +170,8 @@ internal sealed unsafe class VulkanPipeline : IDisposable
                 sType = VkStructureType.PipelineLayoutCreateInfo,
                 setLayoutCount = 1,
                 pSetLayouts = &descLayout,
-                pushConstantRangeCount = 1,
-                pPushConstantRanges = (nint)(&pushConstantRange),
+                pushConstantRangeCount = 2,
+                pPushConstantRanges = (nint)pushConstantRanges,
             };
 
             fixed (VkPipelineLayout* layoutPtr = &PipelineLayout)