Add normal mapping and parallax occlusion mapping for WMO surfaces

Generate normal+height maps from diffuse textures at load time using
luminance-to-height and Sobel 3x3 filtering. Compute per-vertex tangents
via Lengyel's method for TBN basis construction.

Fragment shader uses screen-space UV derivatives (dFdx/dFdy) for smooth
LOD crossfade and angle-adaptive POM sample counts. Flat textures
naturally produce low height variance, causing POM to self-select off.

Settings: Normal Mapping on by default, POM off by default with
Low/Medium/High quality presets. Persisted across sessions.

assets/shaders/wmo.vert.glsl

@@ -21,17 +21,33 @@ layout(location = 0) in vec3 aPos;
 layout(location = 1) in vec3 aNormal;
 layout(location = 2) in vec2 aTexCoord;
 layout(location = 3) in vec4 aColor;
+layout(location = 4) in vec4 aTangent;
 
 layout(location = 0) out vec3 FragPos;
 layout(location = 1) out vec3 Normal;
 layout(location = 2) out vec2 TexCoord;
 layout(location = 3) out vec4 VertColor;
+layout(location = 4) out vec3 Tangent;
+layout(location = 5) out vec3 Bitangent;
 
 void main() {
     vec4 worldPos = push.model * vec4(aPos, 1.0);
     FragPos = worldPos.xyz;
-    Normal = mat3(push.model) * aNormal;
+
+    mat3 normalMatrix = mat3(push.model);
+    Normal = normalMatrix * aNormal;
     TexCoord = aTexCoord;
     VertColor = aColor;
+
+    // Compute TBN basis vectors for normal mapping
+    vec3 T = normalize(normalMatrix * aTangent.xyz);
+    vec3 N = normalize(Normal);
+    // Gram-Schmidt re-orthogonalize
+    T = normalize(T - dot(T, N) * N);
+    vec3 B = cross(N, T) * aTangent.w;
+
+    Tangent = T;
+    Bitangent = B;
+
     gl_Position = projection * view * worldPos;
 }