feat(bbb): answer FetchModelMetadataRequest for brick built models

The client asks for a model's metadata (name, owner, behaviors and its blueprint's
bricks and box) when it shows a brick built model item's tooltip, a model on a
property or an exhibit, and shows BBB_LOADING_BLUEPRINT until it gets it. The
world server never answered. It now does as live did: UG data for the model
(found among the player's items by subkey, else among placed models) and, for a
brick built model, the blueprint data from its ugc row and LXFML.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

dGame/dGameMessages/GameMessageHandler.cpp

@@ -141,6 +141,7 @@ namespace {
 		{ SET_BUILD_MODE, []() { return std::make_unique<SetBuildMode>(); } },
 		{ BUILD_MODE_SET, []() { return std::make_unique<BuildModeSet>(); } },
 		{ UN_USE_BBB_MODEL, []() { return std::make_unique<UnUseBBBModel>(); } },
+		{ FETCH_MODEL_METADATA_REQUEST, []() { return std::make_unique<FetchModelMetadataRequest>(); } },
 		{ BBB_LOAD_ITEM_REQUEST, []() { return std::make_unique<BBBLoadItemRequest>(); } },
 		{ BBB_SAVE_REQUEST, []() { return std::make_unique<BBBSaveRequest>(); } },
 		{ SET_BBB_AUTOSAVE, []() { return std::make_unique<SetBBBAutosave>(); } },