Remove terrain specular and fix washed-out tonemap

Drop specular lighting from terrain shader — ground materials (dirt, grass,
stone) are purely diffuse and specular highlights made them look plastic.
Replace Reinhard tonemapper with a shoulder-only compressor that is identity
below 0.9 and softly rolls off HDR values above, preserving scene contrast.

assets/shaders/terrain.frag

@@ -32,9 +32,6 @@ uniform vec3 uAmbientColor;
 // Camera
 uniform vec3 uViewPos;
 
-// HDR specular
-uniform float uSpecularIntensity;
-
 // Fog
 uniform vec3 uFogColor;
 uniform float uFogStart;
@@ -78,14 +75,8 @@ void main() {
     diff = max(diff, 0.2);  // Minimum light to prevent completely dark faces
     vec3 diffuse = diff * uLightColor * finalColor.rgb;
 
-    // Specular lighting (subtle for terrain)
-    vec3 viewDir = normalize(uViewPos - FragPos);
-    vec3 halfwayDir = normalize(lightDir + viewDir);
-    float spec = pow(max(dot(norm, halfwayDir), 0.0), 32.0);
-    vec3 specular = spec * uLightColor * uSpecularIntensity;
-
-    // Combine lighting
-    vec3 result = ambient + diffuse + specular;
+    // Combine lighting (terrain is purely diffuse — no specular on ground)
+    vec3 result = ambient + diffuse;
 
     // Apply fog
     float distance = length(uViewPos - FragPos);

src/rendering/renderer.cpp

@@ -1176,9 +1176,9 @@ void Renderer::initPostProcess(int w, int h) {
         out vec4 FragColor;
         void main() {
             vec3 color = texture(uScene, vUV).rgb;
-            float exposure = 1.8;
-            color *= exposure;
-            vec3 mapped = color / (color + vec3(1.0));
+            // Shoulder tonemap: identity below 0.9, soft rolloff above
+            vec3 excess = max(color - 0.9, 0.0);
+            vec3 mapped = min(color, vec3(0.9)) + 0.1 * excess / (excess + 0.1);
             FragColor = vec4(mapped, 1.0);
         }
     )";

src/rendering/terrain_renderer.cpp

@@ -324,7 +324,6 @@ void TerrainRenderer::render(const Camera& camera) {
     // Set lighting
     shader->setUniform("uLightDir", glm::vec3(lightDir[0], lightDir[1], lightDir[2]));
     shader->setUniform("uLightColor", glm::vec3(lightColor[0], lightColor[1], lightColor[2]));
-    shader->setUniform("uSpecularIntensity", 0.5f);
     shader->setUniform("uAmbientColor", glm::vec3(ambientColor[0], ambientColor[1], ambientColor[2]));
 
     // Set camera position