Add attribute system with core stats and gameplay components

GameCore/Movement/GravitySystem.cs

@@ -0,0 +1,23 @@
+using GameCore.ECS;
+using GameCore.ECS.Interfaces;
+using GameCore.Physics;
+
+namespace GameCore.Movement;
+
+public class GravitySystem : ISystem
+{
+    public void Update(World world, float deltaTime)
+    {
+        var entities = world.GetEntitiesWith<VelocityComponent>();
+        foreach (var entity in entities)
+        {
+            var velocity = world.GetComponent<VelocityComponent>(entity);
+            var characterState = world.GetComponent<CharacterStateComponent>(entity);
+
+            if (velocity == null || characterState == null)
+                continue;
+
+            if (!characterState.IsOnFloor) velocity.DesiredVelocity.Y -= world.Config.GravityStrength * deltaTime;
+        }
+    }
+}