feat(wallet/account): add show_internally_created filter to SearchAccounts (#332)

Adds optional bool field on SearchAccountsRequest so callers can opt in to
including internally created accounts in search results. Defaults to false
to preserve existing behavior.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: BRBussy

go/wallet/account/v1/service.pb.go

@@ -548,6 +548,12 @@ message SearchAccountsRequest {
       }
     }
   }];
+
+  /*
+     Optional filter to show internally created accounts.
+     False by default.
+  */
+  bool show_internally_created = 5;
 }
 
 /*