Implement comprehensive taxi flight optimizations and proper spline paths

Major improvements:
- Load TaxiPathNode.dbc for actual curved flight paths (no more flying through terrain)
- Add 3-second mounting delay with terrain precaching for entire route
- Implement LOD system for M2 models with distance-based quality reduction
- Add circular terrain loading pattern (13 tiles vs 25, 48% reduction)
- Increase terrain cache from 2GB to 8GB for modern systems

Performance optimizations during taxi:
- Cull small M2 models (boundRadius < 3.0) - not visible from altitude
- Disable particle systems (weather, smoke, M2 emitters) - saves ~7000 particles
- Disable specular lighting on M2 models - saves Blinn-Phong calculations
- Disable shadow mapping on M2 models - saves shadow map sampling and PCF

Technical details:
- Parse TaxiPathNode.dbc spline waypoints for curved paths around terrain
- Build full path from node pairs using TaxiPathEdge lookup
- Precache callback triggers during mounting delay for smooth takeoff
- Circular tile loading uses Euclidean distance check (dx²+dy² <= r²)
- LOD fallback to base mesh when higher LODs unavailable

Result: Buttery smooth taxi flights with no terrain clipping or performance hitches

include/rendering/m2_renderer.hpp

@@ -35,6 +35,7 @@ struct M2ModelGPU {
         uint16_t textureAnimIndex = 0xFFFF; // 0xFFFF = no texture animation
         uint16_t blendMode = 0;   // 0=Opaque, 1=AlphaKey, 2=Alpha, 3=Add, etc.
         uint16_t materialFlags = 0; // M2 material flags (0x01=Unlit, 0x04=TwoSided, 0x10=NoDepthWrite)
+        uint16_t submeshLevel = 0; // LOD level: 0=base, 1=LOD1, 2=LOD2, 3=LOD3
         glm::vec3 center = glm::vec3(0.0f); // Center of batch geometry (model space)
         float glowSize = 1.0f;              // Approx radius of batch geometry
     };
@@ -58,6 +59,7 @@ struct M2ModelGPU {
     bool collisionTreeTrunk = false;
     bool collisionNoBlock = false;
     bool collisionStatue = false;
+    bool isSmallFoliage = false;  // Small foliage (bushes, grass, plants) - skip during taxi
 
     // Collision mesh with spatial grid (from M2 bounding geometry)
     struct CollisionMesh {
@@ -310,9 +312,11 @@ public:
     void clearShadowMap() { shadowEnabled = false; }
 
     void setInsideInterior(bool inside) { insideInterior = inside; }
+    void setOnTaxi(bool onTaxi) { onTaxi_ = onTaxi; }
 
 private:
     bool insideInterior = false;
+    bool onTaxi_ = false;
     pipeline::AssetManager* assetManager = nullptr;
     std::unique_ptr<Shader> shader;