Add shadow toggle (F4) and distance-based WMO group culling

Shadow toggle allows disabling shadow pass for performance testing.
Distance culling skips WMO groups beyond 200 units. Occlusion queries
disabled by default as overhead outweighs benefits in dense scenes.

include/rendering/renderer.hpp

@@ -184,7 +184,13 @@ private:
     glm::mat4 lightSpaceMatrix = glm::mat4(1.0f);
     glm::vec3 shadowCenter = glm::vec3(0.0f);
     bool shadowCenterInitialized = false;
+    bool shadowsEnabled = true;
 
+public:
+    void setShadowsEnabled(bool enabled) { shadowsEnabled = enabled; }
+    bool areShadowsEnabled() const { return shadowsEnabled; }
+
+private:
     void initShadowMap();
     void renderShadowPass();
     uint32_t compileShadowShader();

include/rendering/wmo_renderer.hpp

@@ -428,7 +428,7 @@ private:
     bool frustumCulling = true;
     bool portalCulling = false;  // Disabled by default - needs debugging
     bool distanceCulling = false;  // Disabled - causes ground to disappear
-    bool occlusionCulling = true;  // GPU occlusion queries
+    bool occlusionCulling = false;  // GPU occlusion queries - disabled, adds overhead
     float maxGroupDistance = 500.0f;
     float maxGroupDistanceSq = 250000.0f;  // maxGroupDistance^2
     uint32_t lastDrawCalls = 0;