Add shifting ECB based on bone positions (melee-like)

src/fighter/state/hitstun.rs

@@ -83,7 +83,6 @@ impl FighterStateImpl for HitstunState {
         match self.hitstop_kind {
             HitstopStateKind::Grounded => {}
             HitstopStateKind::Airborne => {
-                ctx.surface.leave_ground();
                 air::integrate_gravity(ctx.velocity, ctx.fighter_attributes, false);
             }
         }
@@ -126,4 +125,13 @@ impl FighterStateImpl for HitstunState {
             HitstopStateKind::Airborne => false,
         }
     }
+
+    fn surface_policy(&self) -> super::SurfacePolicy {
+        match self.hitstop_kind {
+            HitstopStateKind::Grounded => super::SurfacePolicy::Grounded,
+            HitstopStateKind::Airborne => super::SurfacePolicy::Airborne(
+                crate::fighter::surface::EcbLockPolicy::StartOnDetach,
+            ),
+        }
+    }
 }