Async humanoid NPC texture pipeline to eliminate 30-150ms main-thread stalls

Move all DBC lookups (CharSections, ItemDisplayInfo), texture path resolution,
and BLP decoding for humanoid NPCs to background threads. Only GPU texture
uploads remain on the main thread via pre-decoded BLP cache.

include/core/application.hpp

@@ -220,6 +220,7 @@ private:
     std::unordered_set<uint64_t> deadCreatureGuids_;            // GUIDs that should spawn in corpse/death pose
     std::unordered_map<uint32_t, uint32_t> displayIdModelCache_; // displayId → modelId (model caching)
     std::unordered_set<uint32_t> displayIdTexturesApplied_;    // displayIds with per-model textures applied
+    std::unordered_map<uint32_t, std::unordered_map<std::string, pipeline::BLPImage>> displayIdPredecodedTextures_; // displayId → pre-decoded skin textures
     mutable std::unordered_set<uint32_t> warnedMissingDisplayDataIds_; // displayIds already warned
     mutable std::unordered_set<uint32_t> warnedMissingModelPathIds_;   // modelIds/displayIds already warned
     uint32_t nextCreatureModelId_ = 5000;  // Model IDs for online creatures
@@ -312,6 +313,49 @@ private:
     // Deferred equipment compositing queue — processes max 1 per frame to avoid stutter
     std::vector<std::pair<uint64_t, std::pair<std::array<uint32_t, 19>, std::array<uint8_t, 19>>>> deferredEquipmentQueue_;
     void processDeferredEquipmentQueue();
+    // Async equipment texture pre-decode: BLP decode on background thread, composite on main thread
+    struct PreparedEquipmentUpdate {
+        uint64_t guid;
+        std::array<uint32_t, 19> displayInfoIds;
+        std::array<uint8_t, 19> inventoryTypes;
+        std::unordered_map<std::string, pipeline::BLPImage> predecodedTextures;
+    };
+    struct AsyncEquipmentLoad {
+        std::future<PreparedEquipmentUpdate> future;
+    };
+    std::vector<AsyncEquipmentLoad> asyncEquipmentLoads_;
+    void processAsyncEquipmentResults();
+    std::vector<std::string> resolveEquipmentTexturePaths(uint64_t guid,
+        const std::array<uint32_t, 19>& displayInfoIds,
+        const std::array<uint8_t, 19>& inventoryTypes) const;
+    // Deferred NPC texture setup — async DBC lookups + BLP pre-decode to avoid main-thread stalls
+    struct DeferredNpcComposite {
+        uint32_t modelId;
+        uint32_t displayId;
+        // Skin compositing (type-1 slots)
+        std::string basePath;                     // CharSections skin base texture
+        std::vector<std::string> overlayPaths;    // face + underwear overlays
+        std::vector<std::pair<int, std::string>> regionLayers;  // equipment region overlays
+        std::vector<uint32_t> skinTextureSlots;   // model texture slots needing skin composite
+        bool hasComposite = false;                // needs compositing (overlays or equipment regions)
+        bool hasSimpleSkin = false;               // just base skin, no compositing needed
+        // Baked skin (type-1 slots)
+        std::string bakedSkinPath;                // baked texture path (if available)
+        bool hasBakedSkin = false;                // baked skin resolved successfully
+        // Hair (type-6 slots)
+        std::vector<uint32_t> hairTextureSlots;   // model texture slots needing hair texture
+        std::string hairTexturePath;              // resolved hair texture path
+        bool useBakedForHair = false;             // bald NPC: use baked skin for type-6
+    };
+    struct PreparedNpcComposite {
+        DeferredNpcComposite info;
+        std::unordered_map<std::string, pipeline::BLPImage> predecodedTextures;
+    };
+    struct AsyncNpcCompositeLoad {
+        std::future<PreparedNpcComposite> future;
+    };
+    std::vector<AsyncNpcCompositeLoad> asyncNpcCompositeLoads_;
+    void processAsyncNpcCompositeResults();
     // Cache base player model geometry by (raceId, genderId)
     std::unordered_map<uint32_t, uint32_t> playerModelCache_; // key=(race<<8)|gender → modelId
     struct PlayerTextureSlots { int skin = -1; int hair = -1; int underwear = -1; };