Fix quest required item display and add NPC spawn diagnostics

- Fix SMSG_QUESTGIVER_REQUEST_ITEMS: read emoteDelay(u32)+emoteId(u32)+autoFinish(u8)
  instead of 5 uint32s — the 11-byte over-read corrupted requiredMoney, itemCount,
  and all item data (itemId/count/displayInfoId)
- Fix garbled CSV fallback in asset_manager: return nullptr instead of silently
  returning garbled DBC data when binary fallback is unavailable
- Add NPC spawn diagnostics: log when UNIT blocks have displayId=0 (wrong field index)
  and when spawn callback fires with displayId + position
- Improve getModelPathForDisplayId failure logging: distinguish displayDataMap_ miss
  vs modelIdToPath_ miss, and include map sizes for context

src/pipeline/asset_manager.cpp

@@ -300,7 +300,8 @@ std::shared_ptr<DBCFile> AssetManager::loadDBC(const std::string& name) {
                 }
                 LOG_INFO("Binary DBC fallback succeeded: ", name);
             } else {
-                LOG_WARNING("No binary DBC fallback available for: ", name);
+                LOG_ERROR("No binary DBC fallback available for: ", name, " — discarding garbled CSV");
+                return nullptr;
             }
         }
     }