Fix online item GUID resolution, async terrain loading, and inventory enrichment

Enrich online inventory from local DB when server data is incomplete, add
resolveOnlineItemGuid fallback for sell/equip/use, use async enqueueTile for
initial terrain load, improve walk/run animation fallbacks, clear target on
loot close, and broaden equipability detection to include armor/subclass.

include/rendering/terrain_manager.hpp

@@ -143,6 +143,11 @@ public:
      */
     bool loadTile(int x, int y);
 
+    /**
+     * Enqueue a tile for async loading (returns false if previously failed).
+     */
+    bool enqueueTile(int x, int y);
+
     /**
      * Unload a tile
      * @param x Tile X coordinate