refactor: unify session status model

Fixes #5

src/GmRelay.Shared/Domain/SessionStatus.cs

@@ -1,3 +1,5 @@
+using System.Collections.Frozen;
+
 namespace GmRelay.Shared.Domain;
 
 public static class SessionStatus
@@ -6,4 +8,13 @@ public static class SessionStatus
     public const string ConfirmationSent = "ConfirmationSent";
     public const string Confirmed = "Confirmed";
     public const string Cancelled = "Cancelled";
+
+    public static IReadOnlySet<string> All { get; } =
+        new[] { Planned, ConfirmationSent, Confirmed, Cancelled }
+            .ToFrozenSet(StringComparer.Ordinal);
+
+    public static bool IsKnown(string status) => All.Contains(status);
+
+    public static bool IsCancelled(string status) =>
+        string.Equals(status, Cancelled, StringComparison.Ordinal);
 }

src/GmRelay.Shared/Rendering/SessionBatchRenderer.cs

@@ -36,14 +36,10 @@ public static class SessionBatchRenderer
                 messageText += "  <i>Пока никто не записался</i>\n";
             }
 
-            if (session.Status == "Cancelled")
+            if (SessionStatus.IsCancelled(session.Status))
             {
                 messageText += "❌ <i>Сессия отменена</i>\n\n";
             }
-            else if (session.Status == "RecruitmentClosed") 
-            {
-                messageText += "🔒 <i>Набор завершен</i>\n\n";
-            }
             else
             {
                 messageText += "\n";