Store Assistent chats, UI state, and taste in sqlite.

Runtime session data belongs in one DB so History can FTS-search and follow the volume; persona overlays and sidecar cards stay files.

Co-authored-by: Cursor <cursoragent@cursor.com>

SwarmAssistentExtension.cs

@@ -1,6 +1,5 @@
 using System;
 using System.IO;
-using System.Text;
 using System.Text.RegularExpressions;
 using System.Threading.Tasks;
 using Newtonsoft.Json.Linq;