Added mailboxes as local data sources (#1022)

app/MindWork AI Studio/Tools/Databases/IndexStore/MailboxSyncStateEntity.cs

@@ -0,0 +1,29 @@
+namespace AIStudio.Tools.Databases.IndexStore;
+
+/// <summary>
+/// How the sync of a mailbox as a whole stands.
+/// </summary>
+internal sealed class MailboxSyncStateEntity
+{
+    public string DataSourceId { get; set; } = string.Empty;
+
+    /// <summary>
+    /// When the last complete sync of the mailbox ended, or null until one did.
+    /// </summary>
+    public DateTimeOffset? LastSyncCompletedUtc { get; set; }
+
+    /// <summary>
+    /// How many mails a sync would remove from the index at once, held back until the user decides,
+    /// or null when nothing is held back.
+    /// </summary>
+    /// <remarks>
+    /// Nothing on the server is touched either way. But mails removed from the index have to be
+    /// embedded again should they come back, which costs time and, with a cloud provider, money.
+    /// </remarks>
+    public int? PendingRemovalCount { get; set; }
+
+    /// <summary>
+    /// When the user agreed to the held back removal, or null while they did not.
+    /// </summary>
+    public DateTimeOffset? PendingRemovalApprovedUtc { get; set; }
+}