fix: stand-up-on-move and nameplate position tracking

Camera controller / sitting:
- Any movement key (WASD/QE/Space) pressed while sitting now clears the
  sitting flag immediately, matching WoW's sit-to-stand-on-move behaviour
- Added StandUpCallback: when the player stands up via local input the
  callback fires setStandState(0) → CMSG_STAND_STATE_CHANGE(STAND) so
  the server releases the sit lock and restores normal movement
- Fixes character getting stuck in sit state after accidentally
  right-clicking a chair GO in Goldshire Inn (or similar)

Nameplates:
- Use getRenderPositionForGuid() (renderer visual position) as primary
  source for nameplate anchor, falling back to entity X/Y/Z only when
  no render instance exists yet; keeps health bars in sync with the
  rendered model instead of the parallel entity interpolator

src/core/application.cpp

@@ -628,6 +628,11 @@ void Application::setState(AppState newState) {
                         gameHandler->sendMovement(static_cast<game::Opcode>(opcode));
                     }
                 });
+                cc->setStandUpCallback([this]() {
+                    if (gameHandler) {
+                        gameHandler->setStandState(0); // CMSG_STAND_STATE_CHANGE(STAND)
+                    }
+                });
                 cc->setUseWoWSpeed(true);
             }
             if (gameHandler) {