fix: move PlayerAttendanceStats out of interface scope

The record was nested inside ISessionStore, making it ISessionStore.PlayerAttendanceStats.
C# does not infer nested types in return signatures; callers and implementors failed
with CS0246 / CS0738. Moving it to namespace scope resolves the build.

src/GmRelay.Web/Services/ISessionStore.cs

@@ -2,6 +2,19 @@ using GmRelay.Shared.Domain;
 
 namespace GmRelay.Web.Services;
 
+public sealed record PlayerAttendanceStats(
+    Guid PlayerId,
+    string DisplayName,
+    string? TelegramUsername,
+    long TotalSessions,
+    long ConfirmedCount,
+    long DeclinedCount,
+    long NoResponseCount,
+    long WaitlistedCount,
+    long CancellationAffectedCount,
+    decimal AttendanceRate
+);
+
 public interface ISessionStore
 {
     Task<List<WebGameGroup>> GetGroupsForGmAsync(long gmId);
@@ -28,17 +41,4 @@ public interface ISessionStore
     Task<List<WebParticipant>> GetSessionParticipantsAsync(Guid sessionId);
     Task RemovePlayerFromSessionAsync(Guid sessionId, Guid groupId, Guid participantId);
     Task<List<PlayerAttendanceStats>> GetGroupAttendanceStatsAsync(Guid groupId);
-
-public sealed record PlayerAttendanceStats(
-    Guid PlayerId,
-    string DisplayName,
-    string? TelegramUsername,
-    long TotalSessions,
-    long ConfirmedCount,
-    long DeclinedCount,
-    long NoResponseCount,
-    long WaitlistedCount,
-    long CancellationAffectedCount,
-    decimal AttendanceRate
-);
 }