log what actually goes into the snapshot when a unit spawns

the bot's units get models and the player's do not, and both take the
same path through summon() - only owner and position differ, and
position for a player's card comes off the wire. so print the id, the
data row, the owner and the position at the moment the object joins the
battle, and compare the two sides instead of guessing again.

crates/game-service/src/battle_session.rs

@@ -291,6 +291,14 @@ impl BattleSession {
             }
         });
         for entry in due {
+            tracing::info!(
+                tick,
+                global_id = ?entry.global_id.0,
+                data = %entry.data,
+                owner = entry.owner_index(),
+                position = ?entry.position(),
+                "spawning"
+            );
             self.mode.battle.objects.push(entry);
         }
     }