Fix spell cast error messages, action bar drag-drop, and player name display

- Rewrite SpellCastResult enum to match AzerothCore 3.3.5a values (was misaligned, showing wrong error messages like "Not while trading" instead of "Unit not in front")
- Fix spellbook-to-action-bar drag-drop by using ImGuiHoveredFlags_AllowWhenBlockedByActiveItem for cross-window hover detection
- Fix player frame showing wrong character name by looking up activeCharacterGuid instead of always using characters[0]
- Clear playerNameCache on disconnect to prevent stale names across sessions

src/game/game_handler.cpp

@@ -806,6 +806,8 @@ void GameHandler::disconnect() {
         socket.reset();
     }
     activeCharacterGuid_ = 0;
+    playerNameCache.clear();
+    pendingNameQueries.clear();
     setState(WorldState::DISCONNECTED);
     LOG_INFO("Disconnected from world server");
 }