Allow texture load retries instead of permanently caching failures

Remove negative cache for transient load failures in M2, terrain, and
character renderers. Failed textures return white and will be retried
on next model/tile load when assets may have finished streaming.

include/rendering/character_renderer.hpp

@@ -264,7 +264,8 @@ private:
     std::unordered_map<VkTexture*, bool> textureHasAlphaByPtr_;
     std::unordered_map<VkTexture*, bool> textureColorKeyBlackByPtr_;
     std::unordered_map<std::string, VkTexture*> compositeCache_;  // key → texture for reuse
-    std::unordered_set<std::string> failedTextureCache_;  // negative cache for missing textures
+    std::unordered_set<std::string> failedTextureCache_;  // negative cache for budget exhaustion
+    std::unordered_set<std::string> loggedTextureLoadFails_;  // dedup warning logs
     size_t textureCacheBytes_ = 0;
     uint64_t textureCacheCounter_ = 0;
     size_t textureCacheBudgetBytes_ = 1024ull * 1024 * 1024;