Refactor leaderboard logic: incorporate room context into leaderboard stats and channel metadata handling

DorkNet.Server/Data/Entities/LeaderboardChannelMetaEntity.cs

@@ -1,7 +1,8 @@
 namespace DorkNet.Server.Data.Entities;
 
 /// <summary>
-/// Admin-curated metadata for a leaderboard <c>StatChannel</c> id. The
+/// Admin-curated metadata for a room-scoped leaderboard
+/// <c>StatChannel</c> id. The
 /// 2020 watch reports raw integer channel ids via
 /// <c>POST api/Leaderboard/v1/SetStats</c>; this table lets admins map
 /// each channel to a specific room (so the room detail page can list
@@ -9,22 +10,19 @@ namespace DorkNet.Server.Data.Entities;
 /// here override the hardcoded <c>AdminController.KnownStatChannels</c>
 /// fallback. Channels with no row stay listed as "Channel N".
 ///
-/// One channel id, one row. Repeated <c>SetStats</c> calls for the same
-/// channel from any room write to that channel's value rows; the meta
-/// row only changes when an admin renames or re-maps it.
+/// One row per (room, channel). Repeated <c>SetStats</c> calls for the
+/// same channel in different rooms do not share metadata or values.
 /// </summary>
 public class LeaderboardChannelMetaEntity
 {
-    /// <summary>Same int the watch reports for this channel. Primary
-    /// key — there's only ever one meta row per channel.</summary>
-    public int Channel { get; set; }
-
     /// <summary>Room this channel "belongs to" for the per-room detail
-    /// view. 0 = global / unscoped (e.g. cross-room player progression
-    /// counters). The same room can own many channels (e.g. Stunt
-    /// Runner has one channel per course).</summary>
+    /// view. 0 = global / unscoped legacy bucket.</summary>
     public long RoomId { get; set; }
 
+    /// <summary>Same int the watch reports for this channel. Only unique
+    /// together with <see cref="RoomId"/>.</summary>
+    public int Channel { get; set; }
+
     public string Name { get; set; } = string.Empty;
 
     /// <summary>When true, a lower stored value is a better score (race