fix: keep config near the top of saved map json

toMap() emitted config last, so saving a map whose config sat near the top
(e.g. right after the catalogs) moved it to the end. Place config right after
catalogs in the serialized object so its position stays stable.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: kt3k

model/field-block.ts

@@ -705,11 +705,11 @@ export class FieldBlock {
       i: this.#i,
       j: this.#j,
       catalogs: this.#map.catalog.refs,
+      config: this.config,
       actors: this.actorSpawns.toJSON(),
       items: this.itemSpawns.toJSON(),
       props: this.propSpawns.toJSON(),
       field: this.field,
-      config: this.config,
     }, this.#map.catalog)
   }