fix: flip normals when facing away from light/view — fixes cube lighting

Root cause: cube.obj has inconsistent winding order. Many faces have
normals pointing inward (e.g. back face normal = +Z instead of -Z).
With cullMode=None, both sides render, but inward normals cause:
- No diffuse lighting (NdotL < 0 → max() = 0)
- Wrong shadow bias (slope-dependent bias uses wrong NdotL)
- Inconsistent shadow edges on cube faces

Fix: in fragment shader, flip normal if dot(N,L) < 0 or dot(N,V) < 0
This is the standard approach for double-sided rendering with
non-watertight geometry or inconsistent winding order.

imgui.ini

@@ -19,12 +19,12 @@ Size=300,425
 Collapsed=0
 
 [Window][Cortex Engine Debug]
-Pos=60,60
+Pos=1,1
 Size=226,196
 Collapsed=0
 
 [Window][Shadow Parameters]
-Pos=60,60
+Pos=772,456
-Size=318,263
+Size=507,263
 Collapsed=0
 

src/Engine.Graphics.Vulkan/Shaders/triangle.frag

@@ -17,7 +17,7 @@ layout(push_constant) uniform PC {
     vec4 lightPos;
     vec4 lightColor;
     mat4 lightViewProj;
-    vec4 shadowParams; // x=bias, y=sampleRadius, z=farPlane, w=unused
+    vec4 shadowParams;
 } pc;
 
 const vec3 AMBIENT = vec3(0.01, 0.01, 0.02);
@@ -138,6 +138,18 @@ void main()
     float dist = length(toLight);
     vec3 L = toLight / max(dist, 0.001);
 
+    // Flip normal if it faces away from light (fixes inward normals from bad winding)
+    if (dot(N, L) < 0.0)
+    {
+        N = -N;
+    }
+
+    // Also flip for view direction if needed
+    if (dot(N, V) < 0.0)
+    {
+        N = -N;
+    }
+
     float attenuation = pow(clamp(1.0 - dist / max(lightRange, 0.001), 0.0, 1.0), 2.0);
     vec3 radiance = lightColor * lightIntensity * attenuation;