refactor: unify session status model

Fixes #5

src/GmRelay.Bot/Features/Sessions/ExportCalendar/ExportCalendarHandler.cs

@@ -1,5 +1,6 @@
 using System.Text;
 using Dapper;
+using GmRelay.Shared.Domain;
 using Npgsql;
 using Telegram.Bot;
 using Telegram.Bot.Types;
@@ -21,10 +22,10 @@ public sealed class ExportCalendarHandler(
               FROM sessions s
               JOIN game_groups g ON s.group_id = g.id
               WHERE g.telegram_chat_id = @ChatId 
-                AND s.status = 'Planned' 
+                AND s.status = @Planned
                 AND s.scheduled_at > NOW()
               ORDER BY s.scheduled_at ASC",
-            new { ChatId = message.Chat.Id });
+            new { ChatId = message.Chat.Id, Planned = SessionStatus.Planned });
 
         var sessionsList = sessions.ToList();