Add project files.

Database/Entities/Puzzle.cs

@@ -0,0 +1,40 @@
+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; } = [];
+    }
+}