physics: add server flight-back speed override to CameraController

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

include/game/game_handler.hpp

@@ -1156,6 +1156,7 @@ public:
     float getServerSwimSpeed() const { return serverSwimSpeed_; }
     float getServerSwimBackSpeed() const { return serverSwimBackSpeed_; }
     float getServerFlightSpeed() const { return serverFlightSpeed_; }
+    float getServerFlightBackSpeed() const { return serverFlightBackSpeed_; }
     float getServerRunBackSpeed() const { return serverRunBackSpeed_; }
     bool isPlayerRooted() const {
         return (movementInfo.flags & static_cast<uint32_t>(MovementFlags::ROOT)) != 0;

include/rendering/camera_controller.hpp

@@ -96,6 +96,7 @@ public:
     void setSwimSpeedOverride(float speed) { swimSpeedOverride_ = speed; }
     void setSwimBackSpeedOverride(float speed) { swimBackSpeedOverride_ = speed; }
     void setFlightSpeedOverride(float speed) { flightSpeedOverride_ = speed; }
+    void setFlightBackSpeedOverride(float speed) { flightBackSpeedOverride_ = speed; }
     void setRunBackSpeedOverride(float speed) { runBackSpeedOverride_ = speed; }
     void setMovementRooted(bool rooted) { movementRooted_ = rooted; }
     bool isMovementRooted() const { return movementRooted_; }
@@ -284,6 +285,7 @@ private:
     float swimSpeedOverride_ = 0.0f;
     float swimBackSpeedOverride_ = 0.0f;
     float flightSpeedOverride_ = 0.0f;
+    float flightBackSpeedOverride_ = 0.0f;
     float runBackSpeedOverride_ = 0.0f;
     // Server-driven root state: when true, block all horizontal movement input.
     bool movementRooted_ = false;

src/core/application.cpp

@@ -1013,6 +1013,7 @@ void Application::update(float deltaTime) {
                     renderer->getCameraController()->setSwimSpeedOverride(gameHandler->getServerSwimSpeed());
                     renderer->getCameraController()->setSwimBackSpeedOverride(gameHandler->getServerSwimBackSpeed());
                     renderer->getCameraController()->setFlightSpeedOverride(gameHandler->getServerFlightSpeed());
+                    renderer->getCameraController()->setFlightBackSpeedOverride(gameHandler->getServerFlightBackSpeed());
                     renderer->getCameraController()->setRunBackSpeedOverride(gameHandler->getServerRunBackSpeed());
                     renderer->getCameraController()->setMovementRooted(gameHandler->isPlayerRooted());
                     renderer->getCameraController()->setGravityDisabled(gameHandler->isGravityDisabled());

src/rendering/camera_controller.cpp

@@ -722,9 +722,13 @@ void CameraController::update(float deltaTime) {
                 if (flyDescend)    flyMove.z -= 1.0f;
                 if (glm::length(flyMove) > 0.001f) {
                     flyMove = glm::normalize(flyMove);
-                    float flySpeed = (flightSpeedOverride_ > 0.0f && flightSpeedOverride_ < 200.0f
-                                      && !std::isnan(flightSpeedOverride_))
-                                         ? flightSpeedOverride_ : speed;
+                    float flyFwdSpeed = (flightSpeedOverride_ > 0.0f && flightSpeedOverride_ < 200.0f
+                                         && !std::isnan(flightSpeedOverride_))
+                                            ? flightSpeedOverride_ : speed;
+                    float flyBackSpeed = (flightBackSpeedOverride_ > 0.0f && flightBackSpeedOverride_ < 200.0f
+                                          && !std::isnan(flightBackSpeedOverride_))
+                                             ? flightBackSpeedOverride_ : flyFwdSpeed * 0.5f;
+                    float flySpeed = (nowBackward && !nowForward) ? flyBackSpeed : flyFwdSpeed;
                     targetPos += flyMove * flySpeed * physicsDeltaTime;
                 }
                 targetPos.z += verticalVelocity * physicsDeltaTime;