R4: push enrichment — events carry a state delta, kill the last poll

Enrich the in-app live stream into a delta channel so the UI renders a move from the event without a follow-up game.state, and make the matchmaking poll a stream-down fallback.

- pkg/fbs: trailing fields on opponent_moved (move+game+bag_len), your_turn (move_count), match_found (state), game_over (game), notify (account/invitation/state), MoveResult (rack+bag_len); regenerate Go + TS.
- backend: notify owns the FB encoding (encode.go + payload.go input structs); game/lobby/social map their domain types in. emitMove builds the move delta; game.Service.InitialState feeds match_found/game_started the recipient's initial StateView; friends/invitations notify carry their account/invitation. The move-commit response (submit_play/pass/exchange/resign) returns the actor's refilled rack + bag size.
- gateway: MoveResult transcode carries rack+bag_len.
- ui: pure lib/gamedelta.ts reducer advances the per-game cache keyed on move_count (idempotent + gap-safe); app.svelte seeds the cache on match_found/game_started; Game.svelte applies the delta (commit/pass/exchange/resign drop their load()); NewGame polls only while app.streamAlive is false.
- docs: ARCHITECTURE §10, FUNCTIONAL(+ru), backend/gateway/ui READMEs; PRERELEASE R4 marked done + Refinements.

ui/src/gen/fbs/scrabblefb/your-turn-event.ts

@@ -60,8 +60,13 @@ scoreLine(optionalEncoding?:any):string|Uint8Array|null {
   return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
 }
 
+moveCount():number {
+  const offset = this.bb!.__offset(this.bb_pos, 16);
+  return offset ? this.bb!.readInt32(this.bb_pos + offset) : 0;
+}
+
 static startYourTurnEvent(builder:flatbuffers.Builder) {
-  builder.startObject(6);
+  builder.startObject(7);
 }
 
 static addGameId(builder:flatbuffers.Builder, gameIdOffset:flatbuffers.Offset) {
@@ -88,12 +93,16 @@ static addScoreLine(builder:flatbuffers.Builder, scoreLineOffset:flatbuffers.Off
   builder.addFieldOffset(5, scoreLineOffset, 0);
 }
 
+static addMoveCount(builder:flatbuffers.Builder, moveCount:number) {
+  builder.addFieldInt32(6, moveCount, 0);
+}
+
 static endYourTurnEvent(builder:flatbuffers.Builder):flatbuffers.Offset {
   const offset = builder.endObject();
   return offset;
 }
 
-static createYourTurnEvent(builder:flatbuffers.Builder, gameIdOffset:flatbuffers.Offset, deadlineUnix:bigint, opponentNameOffset:flatbuffers.Offset, lastActionOffset:flatbuffers.Offset, lastWordOffset:flatbuffers.Offset, scoreLineOffset:flatbuffers.Offset):flatbuffers.Offset {
+static createYourTurnEvent(builder:flatbuffers.Builder, gameIdOffset:flatbuffers.Offset, deadlineUnix:bigint, opponentNameOffset:flatbuffers.Offset, lastActionOffset:flatbuffers.Offset, lastWordOffset:flatbuffers.Offset, scoreLineOffset:flatbuffers.Offset, moveCount:number):flatbuffers.Offset {
   YourTurnEvent.startYourTurnEvent(builder);
   YourTurnEvent.addGameId(builder, gameIdOffset);
   YourTurnEvent.addDeadlineUnix(builder, deadlineUnix);
@@ -101,6 +110,7 @@ static createYourTurnEvent(builder:flatbuffers.Builder, gameIdOffset:flatbuffers
   YourTurnEvent.addLastAction(builder, lastActionOffset);
   YourTurnEvent.addLastWord(builder, lastWordOffset);
   YourTurnEvent.addScoreLine(builder, scoreLineOffset);
+  YourTurnEvent.addMoveCount(builder, moveCount);
   return YourTurnEvent.endYourTurnEvent(builder);
 }
 }