fix: rendering now works — three critical bugs fixed

1. VkColorComponentFlags: wrong bit values (0x10-0x80 instead of 0x01-0x08)
   → colorWriteMask was 0xF0 instead of 0x0F → no color channels written

2. VkClearValue: was Sequential layout instead of Explicit (union)
   → depthStencil clear value written at wrong offset → depth buffer
   cleared to 0.0 instead of 1.0 → all fragments failed depth test

3. Vulkan clip space correction in vertex shader:
   gl_Position.y = -gl_Position.y (Vulkan Y-down vs OpenGL Y-up)
   gl_Position.z = (gl_Position.z + gl_Position.w) * 0.5 (Z [0,1] vs [-1,1])

Also:
- PushConstantSize fixed from 128 to 144 (two mat4 + vec4)
- Dynamic viewport/scissor state added to pipeline
- Push constants use column_major (default) to match System.Numerics row-major layout
- Camera.GetProjectionMatrix reverted to pure OpenGL-style (correction in shader)
- Screenshots show actual 3D geometry (calibration cubes visible)
- 66/66 tests pass

src/Engine.Graphics.Vulkan/Shaders/vertex.vert

@@ -4,7 +4,7 @@ layout(location = 0) in vec3 inPosition;
 layout(location = 1) in vec3 inColor;
 layout(location = 2) in vec3 inNormal;
 
-layout(row_major, set = 0, binding = 0) uniform FrameUBO {
+layout(set = 0, binding = 0) uniform FrameUBO {
     vec3 cameraPosition;
     uint lightCount;
     vec3 ambientColor;
@@ -27,6 +27,10 @@ void main() {
     vec4 worldPos = pc.model * vec4(inPosition, 1.0);
     gl_Position = pc.mvp * vec4(inPosition, 1.0);
 
+    // Vulkan clip space: Y-down, Z [0,1] — convert from OpenGL Y-up, Z [-1,1]
+    gl_Position.y = -gl_Position.y;
+    gl_Position.z = (gl_Position.z + gl_Position.w) * 0.5;
+
     fragColor = inColor;
     fragNormal = normalize(mat3(pc.model) * inNormal);
     fragWorldPos = worldPos.xyz;