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/game/game_handler.hpp

@@ -1155,6 +1155,7 @@ public:
     float getServerWalkSpeed() const { return serverWalkSpeed_; }
     float getServerSwimSpeed() const { return serverSwimSpeed_; }
     float getServerFlightSpeed() const { return serverFlightSpeed_; }
+    float getServerRunBackSpeed() const { return serverRunBackSpeed_; }
     bool isPlayerRooted() const {
         return (movementInfo.flags & static_cast<uint32_t>(MovementFlags::ROOT)) != 0;
     }