Refactor skill allocation to upgrade; implement skill requirements and resource checks; remove experience from Pet model; update README for skill tree progress

Models/Skill.cs

@@ -1,4 +1,5 @@
 using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
 using System.Text.Json.Serialization;
 
 namespace PetCompanion.Models
@@ -23,16 +24,30 @@ namespace PetCompanion.Models
         public string Name { get; set; }
         public string Description { get; set; }
         public SkillType Type { get; set; }
-        public int PointsCost { get; set; }
         public string Icon { get; set; }
         public List<int>? SkillsIdRequired { get; set; }
+        public virtual ICollection<SkillRequirement> SkillRequirements { get; set; }
         public virtual ICollection<SkillEffect> Effects { get; set; }
         [JsonIgnore]
         public virtual ICollection<PetSkill> PetSkills { get; set; }
     }
 
+    public class SkillRequirement
+    {
+        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
+        [Key]
+        public int Id { get; set; }
+        public int SkillId { get; set; }
+        public string Resource { get; set; }
+        public int Cost { get; set; }
+
+        [JsonIgnore]
+        public virtual Skill Skill { get; set; }
+    }
+
     public class SkillEffect
     {
+        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
         [Key]
         public int Id { get; set; }
         public int SkillId { get; set; }