Added mailboxes as local data sources (#1022)

app/MindWork AI Studio/Tools/Mail/MailBodySource.cs

@@ -0,0 +1,22 @@
+namespace AIStudio.Tools.Mail;
+
+/// <summary>
+/// Which part of a mail its text was read from.
+/// </summary>
+public enum MailBodySource
+{
+    /// <summary>
+    /// No part: the mail is encrypted, or it has no text at all.
+    /// </summary>
+    NONE,
+
+    /// <summary>
+    /// The HTML part, which is what a reader of the mail sees.
+    /// </summary>
+    HTML,
+
+    /// <summary>
+    /// The plain text part, because the mail has no HTML part or nothing visible remains of it.
+    /// </summary>
+    PLAIN_TEXT,
+}