Add per-expansion asset overlay system and fix CharSections DBC layout

Expansion overlays allow each expansion to supplement the base asset data
via an assetManifest field in expansion.json, loaded at priority 50 (below
HD packs). The asset extractor gains --reference-manifest for delta-only
extraction. Also fixes CharSections field indices (VariationIndex=4,
ColorIndex=5, Texture1=6) across all DBC layout references.

src/game/game_handler.cpp

@@ -274,6 +274,7 @@ void GameHandler::update(float deltaTime) {
             auto pkt = InspectPacket::build(guid);
             socket->send(pkt);
             inspectRateLimit_ = 0.75f; // keep it gentle
+            LOG_INFO("Sent CMSG_INSPECT for player 0x", std::hex, guid, std::dec);
         }
     }
 
@@ -5543,6 +5544,7 @@ void GameHandler::updateOtherPlayerVisibleItems(uint64_t guid, const std::map<ui
         // Layout not detected yet — queue this player for inspect as fallback.
         if (socket && state == WorldState::IN_WORLD) {
             pendingAutoInspect_.insert(guid);
+            LOG_INFO("Queued player 0x", std::hex, guid, std::dec, " for auto-inspect (layout not detected)");
         }
         return;
     }