Reduce city stutter: lower spawn rate, resync interval, M2 render distance

- MAX_SPAWNS_PER_FRAME 8→3 (each spawn does sync M2 load, 5-50ms each)
- Creature resync scan interval 1s→3s (O(N) entity iteration)
- M2 render distance: add 1000+ instance tier at 500 units, reduce 2000+
  tier from 350→300 units to cap draw call count in dense cities

include/core/application.hpp

@@ -244,7 +244,7 @@ private:
         float x, y, z, orientation;
     };
     std::vector<PendingCreatureSpawn> pendingCreatureSpawns_;
-    static constexpr int MAX_SPAWNS_PER_FRAME = 8;
+    static constexpr int MAX_SPAWNS_PER_FRAME = 3;
     static constexpr int MAX_NEW_CREATURE_MODELS_PER_FRAME = 1;
     static constexpr uint16_t MAX_CREATURE_SPAWN_RETRIES = 300;
     std::unordered_set<uint64_t> pendingCreatureSpawnGuids_;

src/core/application.cpp

@@ -786,7 +786,7 @@ void Application::update(float deltaTime) {
             if (gameHandler) {
                 static float creatureResyncTimer = 0.0f;
                 creatureResyncTimer += deltaTime;
-                if (creatureResyncTimer >= 1.0f) {
+                if (creatureResyncTimer >= 3.0f) {
                     creatureResyncTimer = 0.0f;
 
                     glm::vec3 playerPos(0.0f);

src/rendering/m2_renderer.cpp

@@ -2081,8 +2081,10 @@ void M2Renderer::render(VkCommandBuffer cmd, VkDescriptorSet perFrameSet, const
 
     lastDrawCallCount = 0;
 
-    // Adaptive render distance: balanced for performance without excessive pop-in
+    // Adaptive render distance: tiered by instance density to cap draw calls
-    const float maxRenderDistance = (instances.size() > 2000) ? 350.0f : 1000.0f;
+    const float maxRenderDistance = (instances.size() > 2000) ? 300.0f
+                                  : (instances.size() > 1000) ? 500.0f
+                                  : 1000.0f;
     const float maxRenderDistanceSq = maxRenderDistance * maxRenderDistance;
     const float fadeStartFraction = 0.75f;
     const glm::vec3 camPos = camera.getPosition();