feat(listsessions): add join/leave buttons for players

For non-managers /listsessions now shows player-friendly actions:
- ✅ Записаться <date> when not registered
- ✖️ Выйти <date> when already active
- ✖️ Выйти из ожидания <date> when waitlisted

Extend SessionListItemDto and the shared SQL query with IsUserActive
and IsUserWaitlisted flags so the renderer can choose the right button.
Update tests to cover all three player states.

src/GmRelay.Bot/Features/Sessions/ListSessions/SessionListMessageRenderer.cs

@@ -23,11 +23,18 @@ internal static class SessionListMessageRenderer
 
     public static IReadOnlyList<PlatformMessageAction> RenderActions(IReadOnlyList<SessionListItemDto> sessions)
     {
-        if (sessions.Count == 0 || !sessions.First().CanManage)
+        if (sessions.Count == 0)
         {
             return [];
         }
 
+        return sessions.First().CanManage
+            ? RenderManagerActions(sessions)
+            : RenderPlayerActions(sessions);
+    }
+
+    private static IReadOnlyList<PlatformMessageAction> RenderManagerActions(IReadOnlyList<SessionListItemDto> sessions)
+    {
         var actions = new List<PlatformMessageAction>();
 
         foreach (var session in sessions)
@@ -60,4 +67,31 @@ internal static class SessionListMessageRenderer
 
         return actions;
     }
+
+    private static IReadOnlyList<PlatformMessageAction> RenderPlayerActions(IReadOnlyList<SessionListItemDto> sessions)
+    {
+        var actions = new List<PlatformMessageAction>();
+
+        foreach (var session in sessions)
+        {
+            var dateTitle = session.ScheduledAt.FormatMoscowShort();
+
+            if (session.IsUserActive || session.IsUserWaitlisted)
+            {
+                actions.Add(new PlatformMessageAction(
+                    $"leave_session:{session.Id}",
+                    session.IsUserWaitlisted ? $"✖️ Выйти из ожидания {dateTitle}" : $"✖️ Выйти {dateTitle}",
+                    $"leave_session:{session.Id}"));
+            }
+            else
+            {
+                actions.Add(new PlatformMessageAction(
+                    $"join_session:{session.Id}",
+                    $"✅ Записаться {dateTitle}",
+                    $"join_session:{session.Id}"));
+            }
+        }
+
+        return actions;
+    }
 }