Fix hair/vendor/loot bugs, revamp spellbook with tabs and icons, clean up action bar, add talent placeholder

- Fix white hair: always override M2 type-6 texture with DBC hair texture when available
- Fix vendor sell: add sellPrice to ItemDef/ItemTemplateRow, use directly instead of empty cache
- Fix empty loot: skip loot window when corpse has no items and no gold
- Revamp spellbook (P key): tabbed UI (General/Active/Passive), spell icons from SpellIcon.dbc, rank text
- Clean up action bar: only auto-populate Attack and Hearthstone, rest assigned via spellbook
- Add talent placeholder (N key): 3-tab window with level/talent point display
- Fix ffplay cleanup: non-blocking waitpid with SIGKILL fallback to prevent orphaned audio processes
- Fix pre-existing getQualityColor visibility for loot window rendering

include/ui/talent_screen.hpp

@@ -0,0 +1,22 @@
+#pragma once
+
+#include "game/game_handler.hpp"
+#include <imgui.h>
+
+namespace wowee {
+namespace ui {
+
+class TalentScreen {
+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 nKeyWasDown = false;
+};
+
+} // namespace ui
+} // namespace wowee