R6(c): drop dead opponent_moved scalars (seat/action/score/total)

These pre-R4 summary scalars on OpponentMovedEvent were redundant with the
move/game delta and read by nobody — the UI codec and mock take only
move/game/bag_len, and the gateway forwards the push payload verbatim. Removed
from scrabble.fbs, the notify emit (notify/events.go) and the round-trip test;
regenerated the FB Go + TS bindings. No prod data, so the wire-slot renumber is
free and there is no DB change.

backend/internal/notify/events.go

@@ -62,20 +62,14 @@ func GameOver(userID, gameID uuid.UUID, result, scoreLine string, game GameSumma
 // OpponentMoved tells userID that move was just committed in game gameID, carrying it as a delta
 // the client applies to its cached game without a refetch: move is the decoded play/pass/
 // exchange, game is the post-move summary (per-seat scores, to_move, move_count, status) and
-// bagLen is the bag size after the draw. The seat/action/score/total scalars repeat the move's
-// summary for wire back-compat.
+// bagLen is the bag size after the draw.
 func OpponentMoved(userID, gameID uuid.UUID, move engine.MoveRecord, game GameSummary, bagLen int) Intent {
 	b := flatbuffers.NewBuilder(512)
 	gid := b.CreateString(gameID.String())
-	act := b.CreateString(move.Action.String())
 	moveOff := buildMoveRecord(b, move)
 	gameOff := buildGameView(b, game)
 	fb.OpponentMovedEventStart(b)
 	fb.OpponentMovedEventAddGameId(b, gid)
-	fb.OpponentMovedEventAddSeat(b, int32(move.Player))
-	fb.OpponentMovedEventAddAction(b, act)
-	fb.OpponentMovedEventAddScore(b, int32(move.Score))
-	fb.OpponentMovedEventAddTotal(b, int32(move.Total))
 	fb.OpponentMovedEventAddMove(b, moveOff)
 	fb.OpponentMovedEventAddGame(b, gameOff)
 	fb.OpponentMovedEventAddBagLen(b, int32(bagLen))