Performance: ring buffer UBOs, batched load screen uploads, background world preloader

- Replace per-frame VMA alloc/free of material UBOs with a ring buffer in
  CharacterRenderer (~500 allocations/frame eliminated)
- Batch all ready terrain tiles into a single GPU upload during load screen
  (processAllReadyTiles instead of one-at-a-time with individual fence waits)
- Lift per-frame creature/GO spawn budgets during load screen warmup phase
- Add background world preloader: saves last world position to disk, pre-warms
  AssetManager file cache with ADT files starting at app init (login screen)
  so terrain workers get instant cache hits when Enter World is clicked
- Distance-filter expensive collision guard to 8-unit melee range
- Merge 3 CharacterRenderer update loops into single pass
- Time-budget instrumentation for slow update stages (>3ms threshold)
- Count-based async creature model upload budget (max 3/frame in-game)
- 1-per-frame game object spawn + per-doodad time budget for transport loading
- Use deque for creature spawn queue to avoid O(n) front-erase

include/core/application.hpp

@@ -6,12 +6,15 @@
 #include <memory>
 #include <string>
 #include <vector>
+#include <deque>
 #include <unordered_map>
 #include <unordered_set>
 #include <array>
 #include <optional>
 #include <future>
 #include <mutex>
+#include <thread>
+#include <atomic>
 
 namespace wowee {
 
@@ -282,7 +285,7 @@ private:
         uint32_t displayId;
         float x, y, z, orientation;
     };
-    std::vector<PendingCreatureSpawn> pendingCreatureSpawns_;
+    std::deque<PendingCreatureSpawn> pendingCreatureSpawns_;
     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;
@@ -353,6 +356,23 @@ private:
     // Quest marker billboard sprites (above NPCs)
     void loadQuestMarkerModels();  // Now loads BLP textures
     void updateQuestMarkers();     // Updates billboard positions
+
+    // Background world preloader — warms AssetManager file cache for the
+    // expected world before the user clicks Enter World.
+    struct WorldPreload {
+        uint32_t mapId = 0;
+        std::string mapName;
+        int centerTileX = 0;
+        int centerTileY = 0;
+        std::atomic<bool> cancel{false};
+        std::vector<std::thread> workers;
+    };
+    std::unique_ptr<WorldPreload> worldPreload_;
+    void startWorldPreload(uint32_t mapId, const std::string& mapName, float serverX, float serverY);
+    void cancelWorldPreload();
+    void saveLastWorldInfo(uint32_t mapId, const std::string& mapName, float serverX, float serverY);
+    struct LastWorldInfo { uint32_t mapId = 0; std::string mapName; float x = 0, y = 0; bool valid = false; };
+    LastWorldInfo loadLastWorldInfo() const;
 };
 
 } // namespace core

include/rendering/character_renderer.hpp

@@ -254,7 +254,14 @@ private:
     VkDescriptorPool materialDescPools_[2] = {VK_NULL_HANDLE, VK_NULL_HANDLE};
     VkDescriptorPool boneDescPool_ = VK_NULL_HANDLE;
     uint32_t lastMaterialPoolResetFrame_ = 0xFFFFFFFFu;
-    std::vector<std::pair<VkBuffer, VmaAllocation>> transientMaterialUbos_[2];
+
+    // Material UBO ring buffer — pre-allocated per frame slot, sub-allocated each draw
+    VkBuffer materialRingBuffer_[2] = {VK_NULL_HANDLE, VK_NULL_HANDLE};
+    VmaAllocation materialRingAlloc_[2] = {VK_NULL_HANDLE, VK_NULL_HANDLE};
+    void* materialRingMapped_[2] = {nullptr, nullptr};
+    uint32_t materialRingOffset_[2] = {0, 0};
+    uint32_t materialUboAlignment_ = 256;  // minUniformBufferOffsetAlignment
+    static constexpr uint32_t MATERIAL_RING_CAPACITY = 4096;
 
     // Texture cache
     struct TextureCacheEntry {