Restructure inventory UI, add vendor selling, camera intro on all spawns, and quest log

Split inventory into bags-only (B key) and character screen (C key). Vendor window
auto-opens bags with sell prices on hover and right-click to sell. Add camera intro
pan on all login/spawn/teleport/hearthstone events and idle orbit after 2 minutes.
Add quest log UI, SMSG_MONSTER_MOVE handling, deferred creature spawn queue, and
creature fade-in/movement interpolation for online mode.

include/ui/game_screen.hpp

@@ -4,6 +4,7 @@
 #include "game/inventory.hpp"
 #include "rendering/world_map.hpp"
 #include "ui/inventory_screen.hpp"
+#include "ui/quest_log_screen.hpp"
 #include "ui/spellbook_screen.hpp"
 #include <imgui.h>
 #include <string>
@@ -143,6 +144,7 @@ private:
     void renderWorldMap(game::GameHandler& gameHandler);
 
     InventoryScreen inventoryScreen;
+    QuestLogScreen questLogScreen;
     SpellbookScreen spellbookScreen;
     rendering::WorldMap worldMap;