SMSG_FORCE_FLIGHT_BACK_SPEED_CHANGE was already ACK'd and stored in
serverFlightBackSpeed_, but the value was never accessible or synced
to the CameraController. Backward flight movement always used forward
flight speed (flightSpeedOverride_), making it faster than the server
intended.
- Add getServerFlightBackSpeed() accessor in GameHandler
- Add flightBackSpeedOverride_ field and setter in CameraController
- Apply it in the fly movement block: backward-only flight uses the
back speed; forward or strafing uses the forward speed as WoW does
- Fallback: 50% of forward flight speed when override is unset
- Sync per-frame in application.cpp alongside the other speed overrides
e2f65dfc59