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/quest_log_screen.hpp

@@ -0,0 +1,21 @@
+#pragma once
+
+#include "game/game_handler.hpp"
+#include <imgui.h>
+
+namespace wowee { namespace ui {
+
+class QuestLogScreen {
+public:
+    void render(game::GameHandler& gameHandler);
+    bool isOpen() const { return open; }
+    void toggle() { open = !open; }
+    void setOpen(bool o) { open = o; }
+
+private:
+    bool open = false;
+    bool lKeyWasDown = false;
+    int selectedIndex = -1;
+};
+
+}} // namespace wowee::ui