Add project files.

Database/Entities/Puzzle.cs

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+namespace ConnectionsAPI.Database.Entities
+{
+    public class Puzzle
+    {
+        /// <summary>
+        /// Primary key of the entity
+        /// </summary>
+        public int Id { get; set; }
+
+        /// <summary>
+        /// When the entity was created (is the sync date)
+        /// </summary>
+        public DateTime CreatedDate { get; set; }
+
+        /// <summary>
+        /// When the puzzle was "printed" online
+        /// </summary>
+        public string PrintDate { get; set; } = string.Empty;
+
+        /// <summary>
+        /// The name of the editor for the puzzle
+        /// </summary>
+        public string EditorName { get; set; } = string.Empty;
+
+        /// <summary>
+        /// The actual count of the puzzle
+        /// </summary>
+        public int Index { get; set; }
+
+        /// <summary>
+        /// The MD5 hash for the source content used to sync this puzzle
+        /// </summary>
+        public string ContentMD5 { get; set; } = string.Empty;
+
+        /// <summary>
+        /// The categories associated with this puzzle
+        /// </summary>
+        public virtual ICollection<PuzzleCategory> Categories { get; set; } = [];
+    }
+}

Database/Entities/PuzzleCard.cs

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+namespace ConnectionsAPI.Database.Entities
+{
+    public class PuzzleCard
+    {
+        /// <summary>
+        /// Primary key of the entity
+        /// </summary>
+        public int Id { get; set; }
+        
+        /// <summary>
+        /// The contents of this card (the word)
+        /// </summary>
+        public string Content { get; set; } = string.Empty;
+
+        /// <summary>
+        /// The initial position of this card on the grid
+        /// </summary>
+        public int Position { get; set; }
+
+        /// <summary>
+        /// The ID of the associated Connections category
+        /// </summary>
+        public int PuzzleCategoryId { get; set; }
+
+        /// <summary>
+        /// The associated category instance
+        /// </summary>
+        public virtual PuzzleCategory? PuzzleCategory { get; set; }
+    }
+}

Database/Entities/PuzzleCategory.cs

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+namespace ConnectionsAPI.Database.Entities
+{
+    public class PuzzleCategory
+    {
+        /// <summary>
+        /// Primary key of the entity
+        /// </summary>
+        public int Id { get; set; }
+
+        /// <summary>
+        /// The name of the category in this Connections puzzle
+        /// </summary>
+        public string Name { get; set; } = string.Empty;
+
+        /// <summary>
+        /// The color of the category in this Connections puzzle; Also used for sorting
+        /// </summary>
+        public PuzzleCategoryColor Color { get; set; }
+
+        /// <summary>
+        /// The ID of the associated Connections puzzle
+        /// </summary>
+        public int PuzzleId { get; set; }
+        
+        /// <summary>
+        /// The associated puzzle instance
+        /// </summary>
+        public virtual Puzzle? Puzzle { get; set; }
+
+        /// <summary>
+        /// The cards associated with this category
+        /// </summary>
+        public ICollection<PuzzleCard> PuzzleCards { get; set; } = [];
+    }
+}

Database/Entities/PuzzleCategoryColor.cs

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+namespace ConnectionsAPI.Database.Entities
+{
+    public enum PuzzleCategoryColor
+    {
+        Yellow = 1,
+        Green = 2,
+        Blue = 3,
+        Purple = 4,
+    }
+}