Added mailboxes as local data sources (#1022)

app/MindWork AI Studio/Settings/DataModel/MailboxAuthMethod.cs

@@ -0,0 +1,23 @@
+namespace AIStudio.Settings.DataModel;
+
+/// <summary>
+/// How AI Studio signs in to an IMAP server.
+/// </summary>
+public enum MailboxAuthMethod
+{
+    /// <summary>
+    /// A method this version of AI Studio does not know, e.g., one written by a newer version. AI Studio never signs in then.
+    /// </summary>
+    /// <remarks>
+    /// It is the member with the underlying value 0 on purpose: when the settings file holds a value
+    /// TolerantEnumConverter cannot read, it falls back to that member. Falling back to a password
+    /// instead would sign in with a secret meant for something else, and every such attempt counts
+    /// as a failed sign-in, which can lock the account.
+    /// </remarks>
+    UNKNOWN = 0,
+
+    /// <summary>
+    /// A username and a password, or an app password where the provider asks for one.
+    /// </summary>
+    PASSWORD,
+}