feat(arena-tk2): split do_matching success into 3007 owner / 3004 joiner

Mirrors prod's TK2 wire flow: the first arriver (parked, picks up cached
pair on a later poll) gets matching_state 3007 (SUCCEEDED_OWNER); the
second arriver (whose poll triggered the pair) gets 3004 (SUCCEEDED).

Observationally inert in the public matching code path today — the
client's Matching class writes isOwner from the response into a field
that nothing in TK2/ranked reads. Matching_Room (private rooms) DOES
read it but from a separate code path that doesn't consult our response.
We send the split anyway for prod fidelity and to leave room for future
flows (rematch UI, etc.) that might start consuming it.

TryPairAsync now returns PairUpResult(Match, IsOwner) instead of bare
PendingMatch?, so the controller can decide owner vs joiner without
re-deriving it.

Also documents on DoMatchingResponseDto why we omit prod's `room_id`
field (not in the client's DoMatchingDetail model; private-room flows
get their room id from a different API and don't consult this response).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.EmulatedEntrypoint/Controllers/ArenaTwoPickBattleController.cs

@@ -75,11 +75,14 @@ public class ArenaTwoPickBattleController : SVSimController
                 });
             }
 
+            // Owner (first arriver, cache hit) gets 3007 = RC_BATTLE_MATCHING_SUCCEEDED_OWNER;
+            // joiner (second arriver who triggered the pair) gets 3004 = RC_BATTLE_MATCHING_SUCCEEDED.
+            // See PairUpResult docs for why this split is observationally inert in TK2 today.
             return Ok(new DoMatchingResponseDto
             {
-                MatchingState = 3004,
-                BattleId = paired.BattleId,
-                NodeServerUrl = paired.NodeServerUrl,
+                MatchingState = paired.IsOwner ? 3007 : 3004,
+                BattleId = paired.Match.BattleId,
+                NodeServerUrl = paired.Match.NodeServerUrl,
             });
         }
         catch (ArenaTwoPickException ex)