physics: implement HOVER movement flag physics in CameraController

When the server sets MovementFlags::HOVER (SMSG_MOVE_SET_HOVER), the
player now floats 4 yards above the nearest ground surface instead of
standing on it. Uses the existing floor-snap path with a HOVER_HEIGHT
offset applied to the snap target.

- game_handler.hpp: add isHovering() accessor (reads HOVER flag from
  movementInfo.flags, which is already set by handleForceMoveFlagChange)
- camera_controller.hpp: add hoverActive_ field and setHoverActive()
- camera_controller.cpp: apply HOVER_HEIGHT = 4.0f offset at floor snap
- application.cpp: sync hover state each frame alongside other movement
  states (gravity, feather fall, water walk, flying)

src/rendering/camera_controller.cpp

@@ -1249,7 +1249,10 @@ void CameraController::update(float deltaTime) {
                                    dz >= -0.25f && dz <= stepUp * 1.5f);
 
                 if (dz >= -fallCatch && (nearGround || airFalling || slopeGrace)) {
-                    targetPos.z = *groundH;
+                    // HOVER: float at fixed height above ground instead of standing on it
+                    static constexpr float HOVER_HEIGHT = 4.0f;  // ~4 yards above ground
+                    const float snapH = hoverActive_ ? (*groundH + HOVER_HEIGHT) : *groundH;
+                    targetPos.z = snapH;
                     verticalVelocity = 0.0f;
                     grounded = true;
                     lastGroundZ = *groundH;