fix(cdn): serve baked RRO rooms a loadable stub blob (version 16, save skeleton)

An enabled baked room still had no Maker Pen: the client fetched the CDN's
synthetic stub for room_{id}_dorknet_v8.dat and silently loaded the room
with no room roles. Measured against Rec Center's working room_100_v1.dat
(10,930 bytes, the same client loads it with Maker Pen), the old 1,872-byte
roles-only stub was stamped PersistedRoomVersion 19 — past the March-2023
client's ceiling of 16, which only the S3-hit path clamped — and lacked the
skeleton every real save carries (last_save_time, activity_id = the room's
LocationReplicationId, connectable graph, scene settings, object model,
room_mood_* blocks).

RoomDataBlobService.BuildRroEditableBlob now emits that skeleton per room
at version 16 (untyped fields appended on the wire; payloads are Rec
Center's defaults verbatim). CdnController resolves the RRO room for the
miss path, passes its location id, and clamps synthesised blobs the same
way it clamps S3 hits. Tests pin version 16, the activity id and
CanUseMakerPen on every role.

DorkNet.Server.Tests/RroRoomBlobTests.cs

@@ -54,6 +54,7 @@ public sealed class RroRoomBlobTests : IClassFixture<DorkNetServerFactory>
                 IsAGRoom = true,
                 TagsCsv = "recroomoriginal,sport",
                 CurrentDataBlobName = string.Empty,
+                LocationReplicationId = "b010171f-4875-4e89-baba-61e878cd41e1",
             });
             db.RoomScenes.Add(new RoomSceneEntity
             { RoomId = roomId, Name = "Home", OrderIndex = 0, DataBlobName = string.Empty });
@@ -102,6 +103,14 @@ public sealed class RroRoomBlobTests : IClassFixture<DorkNetServerFactory>
         var persisted = PersistedRoomData.Parser.ParseFrom(blobBytes);
         Assert.NotNull(persisted.RoomRoleData);
         Assert.NotEmpty(persisted.RoomRoleData.RoomRoles);
+        Assert.True(persisted.RoomRoleData.RoomRoles.All(r => r.CanUseMakerPen is { Overrides: true, InnerValue: true }));
+
+        // The March-2023 client rejects a blob past PersistedRoomVersion 16
+        // (the old stub was stamped 19 and loaded as "no room data"), and a
+        // real save carries the room's location id as activity_id. Our proto
+        // doesn't type activity_id, so look for it on the wire.
+        Assert.Equal(RoomDataBlobService.Client2023MaxPersistedRoomVersion, (int)persisted.Version);
+        Assert.Contains("b010171f-4875-4e89-baba-61e878cd41e1", System.Text.Encoding.UTF8.GetString(blobBytes));
 
         // ── reset: back to scene-only ───────────────────────────────────────
         var reset = await PostJsonAsync(adminClient, $"/api/admin/v1/rooms/{roomId}/subrooms/0/blob/reset");