Added backups of all data, restorable on another computer (#1008)

Co-authored-by: Thorsten Sommer <SommerEngineering@users.noreply.github.com>

app/MindWork AI Studio/Chat/FileAttachmentImage.cs

@@ -1,3 +1,5 @@
+using System.Text.Json.Serialization;
+
 namespace AIStudio.Chat;
 
 public record FileAttachmentImage(string FileName, string FilePath, long FileSizeBytes) : FileAttachment(FileAttachmentType.IMAGE, FileName, FilePath, FileSizeBytes), IImageSource
@@ -13,5 +15,18 @@ public record FileAttachmentImage(string FileName, string FilePath, long FileSiz
     /// <summary>
     /// The image source.
     /// </summary>
+    /// <remarks>
+    /// An attached image is a file, so its source is the path of that file. It is not stored a second
+    /// time: the stored file path is relative when the image lies below the data directory, and the
+    /// source has to follow it when the chat is read again, on whatever computer that happens.
+    /// </remarks>
+    [JsonIgnore]
     public string Source { get; set; } = FilePath;
+
+    /// <inheritdoc />
+    public override FileAttachment WithFilePath(string filePath) => new FileAttachmentImage(this.FileName, filePath, this.FileSizeBytes)
+    {
+        SourceType = this.SourceType,
+        Source = this.SourceType is ContentImageSource.LOCAL_PATH ? filePath : this.Source,
+    };
 }