Add per-group spatial grid for WMO collision and reduce collision call frequency

Build a 2D triangle grid per WMO group at load time so getFloorHeight and
checkWallCollision only test triangles in nearby cells instead of brute-forcing
all triangles. Also reduce sweep steps (12→4), ground probes (3→1), camera
floor probes (5→2), throttle isInsideWMO to every 10 frames, and early-out
wall collision on first hit.

include/rendering/camera_controller.hpp

@@ -133,6 +133,11 @@ private:
     static constexpr float JUMP_BUFFER_TIME = 0.15f;  // 150ms input buffer
     static constexpr float COYOTE_TIME = 0.10f;        // 100ms grace after leaving ground
 
+    // Cached isInsideWMO result (throttled to avoid per-frame cost)
+    bool cachedInsideWMO = false;
+    int insideWMOCheckCounter = 0;
+    glm::vec3 lastInsideWMOCheckPos = glm::vec3(0.0f);
+
     // Swimming
     bool swimming = false;
     bool wasSwimming = false;

include/rendering/wmo_renderer.hpp

@@ -270,6 +270,25 @@ private:
         // Collision geometry (positions only, for floor raycasting)
         std::vector<glm::vec3> collisionVertices;
         std::vector<uint16_t> collisionIndices;
+
+        // 2D spatial grid for fast triangle lookup (built at load time).
+        // Bins triangles by their XY bounding box into grid cells.
+        static constexpr float COLLISION_CELL_SIZE = 4.0f;
+        int gridCellsX = 0;
+        int gridCellsY = 0;
+        glm::vec2 gridOrigin;  // XY of bounding box min
+        // cellTriangles[cellY * gridCellsX + cellX] = list of triangle start indices
+        std::vector<std::vector<uint32_t>> cellTriangles;
+
+        // Build the spatial grid from collision geometry
+        void buildCollisionGrid();
+
+        // Get triangle indices for a local-space XY point
+        const std::vector<uint32_t>* getTrianglesAtLocal(float localX, float localY) const;
+
+        // Get triangle indices for a local-space XY range (for wall collision)
+        void getTrianglesInRange(float minX, float minY, float maxX, float maxY,
+                                 std::vector<uint32_t>& out) const;
     };
 
     /**
@@ -497,6 +516,7 @@ private:
     std::unordered_map<GridCell, std::vector<uint32_t>, GridCellHash> spatialGrid;
     std::unordered_map<uint32_t, size_t> instanceIndexById;
     mutable std::vector<size_t> candidateScratch;
+    mutable std::vector<uint32_t> wallTriScratch;  // Scratch for wall collision grid queries
     mutable std::unordered_set<uint32_t> candidateIdScratch;
 
     // Parallel visibility culling