test: extend TelegramSessionBatchRendererTests with regression cases

- Empty sessions
- HTML encoding in title
- Confirmed status buttons
- No join link handling

Issue: #33

tests/GmRelay.Bot.Tests/Rendering/SessionBatchViewBuilderTests.cs

@@ -114,7 +114,7 @@ public sealed class SessionBatchViewBuilderTests
     [Fact]
     public void Build_ShouldHandleEmptySessions()
     {
-        var result = SessionBatchViewBuilder.Build("Empty", [], []);
+        var result = SessionBatchViewBuilder.Build("Empty", Array.Empty<SessionBatchDto>(), Array.Empty<ParticipantBatchDto>());
         Assert.Equal("Empty", result.Title);
         Assert.Empty(result.Sessions);
     }
@@ -130,6 +130,10 @@ public sealed class SessionBatchViewBuilderTests
 
         Assert.Equal(SessionStatus.Confirmed, result.Sessions[0].Status);
         Assert.Equal(2, result.Sessions[0].AvailableActions.Count);
+        Assert.Equal("join_session", result.Sessions[0].AvailableActions[0].ActionKey);
+        Assert.Equal("leave_session", result.Sessions[0].AvailableActions[1].ActionKey);
+        Assert.Equal(sessionId, result.Sessions[0].AvailableActions[0].SessionId);
+        Assert.Equal(sessionId, result.Sessions[0].AvailableActions[1].SessionId);
     }
 
     [Fact]
@@ -142,6 +146,7 @@ public sealed class SessionBatchViewBuilderTests
         var result = SessionBatchViewBuilder.Build("Test", sessions, participants);
 
         Assert.Null(result.Sessions[0].MaxPlayers);
-        Assert.Equal(0, result.Sessions[0].ActivePlayerCount);
+        var joinAction = result.Sessions[0].AvailableActions.First(a => a.ActionKey == "join_session");
+        Assert.DoesNotContain("ожидания", joinAction.Label);
     }
 }