Add spellbook, fix WMO floor clipping, and polish UI/visuals

- Add spellbook screen (P key) with Spell.dbc name lookup and action bar assignment
- Default Attack and Hearthstone spells available in single player
- Fix WMO floor clipping (gryphon roost) by tightening ceiling rejection threshold
- Darken ocean water, increase wave motion and opacity
- Add M2 model distance fade-in to prevent pop-in
- Reposition chat window, add slash/enter key focus
- Remove debug key commands (keep only F1 perf HUD, N minimap)
- Performance: return chat history by const ref, use deque for O(1) pop_front

include/ui/game_screen.hpp

@@ -3,6 +3,7 @@
 #include "game/game_handler.hpp"
 #include "game/inventory.hpp"
 #include "ui/inventory_screen.hpp"
+#include "ui/spellbook_screen.hpp"
 #include <imgui.h>
 #include <string>
 
@@ -110,6 +111,7 @@ private:
      * Inventory screen
      */
     InventoryScreen inventoryScreen;
+    SpellbookScreen spellbookScreen;
 };
 
 }} // namespace wowee::ui