Hygiene B4c: clean dedup helpers (knockback, bakers, editor rig)

- KnockbackUtil.Stamp: shared knockback-stamp used by AbilityFireSystem + MeleeComboSystem (guard + planar normalize + write; speed passed in).
- BakerStructureExt: AddPlacedStructure/AddDamageable extensions on Baker<T>; rewired Turret/Structure/Harvester/Conveyor/Fabricator bakers (baked data + serialized fields unchanged).
- EnemyPrefabBakeExt.AddEnemyPrefabPool: shared prefab-buffer bake for ZoneEnemyDirector/WaveDirector authoring (fields stay flat — no serialization change).
- Editor AnimRigUtil (HasParam + root-yaw overlay clip) shared by PlayerRigTools/EnemyRigTools; EnemyRigTools.MakeMat now GUID-preserving (CopySerialized over existing) — the composite AnimatorController copy left as-is with a caveat comment.

466/466 EditMode tests pass, 0 warnings.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Assets/_Project/Scripts/Authoring/Building/StructureAuthoring.cs

@@ -24,19 +24,11 @@ namespace ProjectM.Authoring
             public override void Bake(StructureAuthoring authoring)
             {
                 var entity = GetEntity(authoring, TransformUsageFlags.Dynamic);
-                AddComponent(entity, new PlacedStructure
-                {
-                    Type = authoring.Kind,
-                    Cell = default,
-                    NextTick = 0u,
-                    LastProcessedTick = 0u,
-                });
+                this.AddPlacedStructure(entity, authoring.Kind);
                 // EB-1: Wall/Pylon are damageable + destructible AI targets (a wall soaks Husk strikes that would
                 // otherwise hit a turret). DamageEvent buffer MUST exist or an AI strike crashes at ECB playback.
                 // No HitRadius -> ProjectileDamageSystem ignores them (no friendly projectile fire).
-                AddComponent(entity, new Health { Current = authoring.MaxHp, Max = authoring.MaxHp });
-                AddBuffer<DamageEvent>(entity);
-                AddComponent<Destructible>(entity);
+                this.AddDamageable(entity, authoring.MaxHp);
             }
         }
     }