RHI: Add Compute/Dispatch unit tests (P1-7) and fix shader type bugs

Bug fixes:
- D3D12Shader::Compile: Set m_type based on target string (cs_/vs_/ps_/gs_)
- OpenGLShader::Compile: Parse target parameter to determine shader type
- OpenGLShader::CompileCompute: Set m_type = ShaderType::Compute
- D3D12CommandList::SetPipelineState: Use correct PSO handle for Compute

New tests (test_compute.cpp, 8 tests):
- ComputeShader_Compile_ValidShader
- ComputeShader_GetType_ReturnsCompute
- ComputeShader_Shutdown_Invalidates
- PipelineState_SetComputeShader
- PipelineState_HasComputeShader_ReturnsTrue
- PipelineState_GetType_Compute
- PipelineState_EnsureValid_Compute
- CommandList_Dispatch_Basic

Test results: 232/232 passed (D3D12: 116, OpenGL: 116)

engine/src/RHI/D3D12/D3D12Shader.cpp

@@ -55,6 +55,16 @@ bool D3D12Shader::Compile(const void* sourceData, size_t sourceSize, const char*
         return false;
     }
 
+    if (strstr(target, "vs_")) {
+        m_type = ShaderType::Vertex;
+    } else if (strstr(target, "ps_")) {
+        m_type = ShaderType::Fragment;
+    } else if (strstr(target, "gs_")) {
+        m_type = ShaderType::Geometry;
+    } else if (strstr(target, "cs_")) {
+        m_type = ShaderType::Compute;
+    }
+
     m_uniformsCached = false;
     return true;
 }