fix(arena-tk2): park returns 3002 RETRY + empty node_server_url

Two client-crash bugs in the do_matching response when no partner is
waiting:

1. matching_state was 3001 (RC_BATTLE_MATCHING_ILLEGAL); the client's
   Matching.OnFinishedDoMatching switch maps that to an error dialog,
   not a retry. The retry state is 3002 (RC_BATTLE_MATCHING_RETRY).

2. node_server_url was omitted entirely. The client's
   DoMatchingBase.SettingDoMatchingData reads it via
   data["node_server_url"].ToString() with no Keys.Contains guard, so
   absence throws KeyNotFoundException out of NetworkManager.Connect
   before the matching_state switch is even reached. Prod RETRY
   captures send "" while waiting and the real URL only on SUCCEEDED;
   match that.

battle_id stays absent; its accessor IS guarded.

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

SVSim.EmulatedEntrypoint/Controllers/ArenaTwoPickBattleController.cs

@@ -62,10 +62,16 @@ public class ArenaTwoPickBattleController : SVSimController
                 ct);
             if (paired is null)
             {
+                // 3002 = RC_BATTLE_MATCHING_RETRY: client polls again. 3001 is ILLEGAL
+                // and shows an error dialog on the client side. node_server_url must be
+                // present (the client's DoMatchingBase.SettingDoMatchingData calls
+                // .ToString() on it without a Keys.Contains guard); prod sends "" while
+                // waiting and the real URL only on SUCCEEDED. battle_id stays absent
+                // (its accessor IS guarded).
                 return Ok(new DoMatchingResponseDto
                 {
-                    MatchingState = 3001,
-                    // BattleId / NodeServerUrl null — client polls again.
+                    MatchingState = 3002,
+                    NodeServerUrl = "",
                 });
             }