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.

pkg/fbs/scrabble.fbs

@@ -510,14 +510,9 @@ table GameOverEvent {
 // OpponentMovedEvent carries a move another seat just committed as a delta the client applies to
 // its cached game without a refetch: move is the decoded play/pass/exchange (the same record
 // game.history returns), game is the post-move summary (per-seat scores, to_move, move_count,
-// status) and bag_len is the bag size after the draw. The leading seat/action/score/total scalars
-// are the older summary, now redundant with move/game and kept only for wire back-compat.
+// status) and bag_len is the bag size after the draw.
 table OpponentMovedEvent {
   game_id:string;
-  seat:int;
-  action:string;
-  score:int;
-  total:int;
   move:MoveRecord;
   game:GameView;
   bag_len:int;