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/io/src/main/scala/de/nowchess/io/fen/FenParser.scala

@@ -11,16 +11,27 @@ object FenParser extends GameContextImport:
     */
   def parseFen(fen: String): Either[GameError, GameContext] =
     val parts = fen.trim.split("\\s+")
-    if parts.length != 6 then Left(GameError.ParseError(s"Invalid FEN: expected 6 space-separated fields, got ${parts.length}"))
+    if parts.length != 6 then
+      Left(GameError.ParseError(s"Invalid FEN: expected 6 space-separated fields, got ${parts.length}"))
     else
       for
-        board          <- parseBoard(parts(0)).toRight(GameError.ParseError("Invalid FEN: invalid board position"))
-        activeColor    <- parseColor(parts(1)).toRight(GameError.ParseError("Invalid FEN: invalid active color (expected 'w' or 'b')"))
+        board <- parseBoard(parts(0)).toRight(GameError.ParseError("Invalid FEN: invalid board position"))
+        activeColor <- parseColor(parts(1)).toRight(
+          GameError.ParseError("Invalid FEN: invalid active color (expected 'w' or 'b')"),
+        )
         castlingRights <- parseCastling(parts(2)).toRight(GameError.ParseError("Invalid FEN: invalid castling rights"))
-        enPassant      <- parseEnPassant(parts(3)).toRight(GameError.ParseError("Invalid FEN: invalid en passant square"))
-        halfMoveClock  <- parts(4).toIntOption.toRight(GameError.ParseError("Invalid FEN: invalid half-move clock (expected integer)"))
-        fullMoveNumber <- parts(5).toIntOption.toRight(GameError.ParseError("Invalid FEN: invalid full move number (expected integer)"))
-        _              <- Either.cond(halfMoveClock >= 0 && fullMoveNumber >= 1, (), GameError.ParseError("Invalid FEN: invalid move counts"))
+        enPassant <- parseEnPassant(parts(3)).toRight(GameError.ParseError("Invalid FEN: invalid en passant square"))
+        halfMoveClock <- parts(4).toIntOption.toRight(
+          GameError.ParseError("Invalid FEN: invalid half-move clock (expected integer)"),
+        )
+        fullMoveNumber <- parts(5).toIntOption.toRight(
+          GameError.ParseError("Invalid FEN: invalid full move number (expected integer)"),
+        )
+        _ <- Either.cond(
+          halfMoveClock >= 0 && fullMoveNumber >= 1,
+          (),
+          GameError.ParseError("Invalid FEN: invalid move counts"),
+        )
       yield GameContext(
         board = board,
         turn = activeColor,

modules/io/src/main/scala/de/nowchess/io/service/dto/CombinedExportResponse.scala

@@ -0,0 +1,3 @@
+package de.nowchess.io.service.dto
+
+final case class CombinedExportResponse(fen: String, pgn: String)

modules/io/src/main/scala/de/nowchess/io/service/resource/IoResource.scala

@@ -3,7 +3,7 @@ package de.nowchess.io.service.resource
 import de.nowchess.api.game.GameContext
 import de.nowchess.io.fen.{FenExporter, FenParser}
 import de.nowchess.io.pgn.{PgnExporter, PgnParser}
-import de.nowchess.io.service.dto.{ImportFenRequest, ImportPgnRequest, IoErrorDto}
+import de.nowchess.io.service.dto.{CombinedExportResponse, ImportFenRequest, ImportPgnRequest, IoErrorDto}
 import io.smallrye.mutiny.Uni
 import jakarta.enterprise.context.ApplicationScoped
 import jakarta.ws.rs.*
@@ -75,3 +75,18 @@ class IoResource:
   @APIResponse(responseCode = "200", description = "PGN text")
   def exportPgn(ctx: GameContext): Uni[Response] =
     Uni.createFrom().item(Response.ok(PgnExporter.exportGameContext(ctx)).build())
+
+  @POST
+  @Path("/export/combined")
+  @Consumes(Array(MediaType.APPLICATION_JSON))
+  @Produces(Array(MediaType.APPLICATION_JSON))
+  @Operation(summary = "Export FEN and PGN", description = "Serialize a GameContext to both FEN and PGN in one call")
+  @APIResponse(responseCode = "200", description = "FEN and PGN")
+  def exportCombined(ctx: GameContext): Uni[Response] =
+    Uni
+      .createFrom()
+      .item(
+        Response
+          .ok(CombinedExportResponse(FenExporter.exportGameContext(ctx), PgnExporter.exportGameContext(ctx)))
+          .build(),
+      )