perf(core): reduce inter-service HTTP calls from 11 to 4 per move

- Add `postMoveStatus` batch method to `RuleSet` trait (default impl composes
  individual calls; `RuleSetRestAdapter` overrides with single HTTP round-trip)
- Collapse 5 sequential rule checks in `GameEngine.executeMove` into one
  `postMoveStatus` call
- Add `POST /api/rules/post-move-status` endpoint to rule-service
- Add `exportCombined` to `IoServiceClient` and `POST /io/export/combined`
  endpoint to io-service, replacing two separate FEN/PGN HTTP calls
- Fix `statusOf` to pattern-match on `WinReason` from `ctx.result` instead
  of making a redundant `isCheckmate` HTTP call
- Remove duplicate `legalMoves` pre-validation in `GameResource.makeMove`;
  engine already validates and fires `InvalidMoveEvent`
- Add `scalafix:off` guards for pre-existing `var`/`return` usage in
  `DefaultRules` hot-path code
- Apply spotless formatting to previously unformatted files

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

modules/json/src/main/scala/de/nowchess/json/GameResultDeserializer.scala

@@ -11,7 +11,7 @@ class GameResultDeserializer extends JsonDeserializer[GameResult]:
   override def deserialize(p: JsonParser, ctx: DeserializationContext): GameResult =
     val node = p.getCodec.readTree[ObjectNode](p)
     node.get("type").asText() match
-      case "win"  =>
+      case "win" =>
         GameResult.Win(
           Color.valueOf(node.get("color").asText()),
           WinReason.valueOf(node.get("winReason").asText()),