physics: sync all server movement speeds to CameraController

Previously only run speed was synced. Now all server-driven movement
speeds are forwarded to the camera controller each frame:
- runSpeedOverride_: server run speed (existing)
- walkSpeedOverride_: server walk speed (Ctrl key movement)
- swimSpeedOverride_: swim speed (Swim Form, Engineering fins)
- flightSpeedOverride_: flight speed (epic vs normal flying mounts)
- runBackSpeedOverride_: back-pedal speed

Each uses the server value when non-zero/sane, falling back to the
hardcoded WoW default constant otherwise.

include/rendering/camera_controller.hpp

@@ -95,6 +95,7 @@ public:
     void setWalkSpeedOverride(float speed) { walkSpeedOverride_ = speed; }
     void setSwimSpeedOverride(float speed) { swimSpeedOverride_ = speed; }
     void setFlightSpeedOverride(float speed) { flightSpeedOverride_ = speed; }
+    void setRunBackSpeedOverride(float speed) { runBackSpeedOverride_ = speed; }
     void setMovementRooted(bool rooted) { movementRooted_ = rooted; }
     bool isMovementRooted() const { return movementRooted_; }
     void setGravityDisabled(bool disabled) { gravityDisabled_ = disabled; }
@@ -280,6 +281,7 @@ private:
     float walkSpeedOverride_ = 0.0f;
     float swimSpeedOverride_ = 0.0f;
     float flightSpeedOverride_ = 0.0f;
+    float runBackSpeedOverride_ = 0.0f;
     // Server-driven root state: when true, block all horizontal movement input.
     bool movementRooted_ = false;
     // Server-driven gravity disable (levitate/hover): skip gravity accumulation.