Stage 17 round 6 (#4/#5/#6): draft persistence wire + gateway + UI

Complete the client-side draft feature on top of the shipped backend
foundation (the game_drafts store/service):

- FB: DraftRequest{game_id,json} + DraftView{json} (a draft get reuses
  GameActionRequest); regenerated committed Go + TS bindings.
- Backend REST: GET/PUT /games/:id/draft, a draftDTO
  (rack_order/board_tiles) mapped to game.Draft.
- Gateway: draft.get/draft.save transcode forwarding the composition
  JSON verbatim (json.RawMessage both ways -- no double-encode).
- UI: debounced save of the rack order + board tiles and restore on
  load (lib/draft.ts), plus #5 -- tiles may be arranged on the
  opponent's turn (placement relaxed; the preview and Make-move stay
  your-turn-only, so an off-turn draft is position-only).

Tests: backend handler validation, gateway pass-through round-trip, UI
draft/codec units, and a draft-restore e2e.

ui/src/gen/fbs/scrabblefb.ts

@@ -10,6 +10,8 @@ export { ChatPostRequest } from './scrabblefb/chat-post-request.js';
 export { CheckWordRequest } from './scrabblefb/check-word-request.js';
 export { ComplaintRequest } from './scrabblefb/complaint-request.js';
 export { CreateInvitationRequest } from './scrabblefb/create-invitation-request.js';
+export { DraftRequest } from './scrabblefb/draft-request.js';
+export { DraftView } from './scrabblefb/draft-view.js';
 export { EmailLoginRequest } from './scrabblefb/email-login-request.js';
 export { EmailRequestRequest } from './scrabblefb/email-request-request.js';
 export { EnqueueRequest } from './scrabblefb/enqueue-request.js';

ui/src/gen/fbs/scrabblefb/draft-request.ts

@@ -0,0 +1,60 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import * as flatbuffers from 'flatbuffers';
+
+export class DraftRequest {
+  bb: flatbuffers.ByteBuffer|null = null;
+  bb_pos = 0;
+  __init(i:number, bb:flatbuffers.ByteBuffer):DraftRequest {
+  this.bb_pos = i;
+  this.bb = bb;
+  return this;
+}
+
+static getRootAsDraftRequest(bb:flatbuffers.ByteBuffer, obj?:DraftRequest):DraftRequest {
+  return (obj || new DraftRequest()).__init(bb.readInt32(bb.position()) + bb.position(), bb);
+}
+
+static getSizePrefixedRootAsDraftRequest(bb:flatbuffers.ByteBuffer, obj?:DraftRequest):DraftRequest {
+  bb.setPosition(bb.position() + flatbuffers.SIZE_PREFIX_LENGTH);
+  return (obj || new DraftRequest()).__init(bb.readInt32(bb.position()) + bb.position(), bb);
+}
+
+gameId():string|null
+gameId(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+gameId(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 4);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+json():string|null
+json(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+json(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 6);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+static startDraftRequest(builder:flatbuffers.Builder) {
+  builder.startObject(2);
+}
+
+static addGameId(builder:flatbuffers.Builder, gameIdOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(0, gameIdOffset, 0);
+}
+
+static addJson(builder:flatbuffers.Builder, jsonOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(1, jsonOffset, 0);
+}
+
+static endDraftRequest(builder:flatbuffers.Builder):flatbuffers.Offset {
+  const offset = builder.endObject();
+  return offset;
+}
+
+static createDraftRequest(builder:flatbuffers.Builder, gameIdOffset:flatbuffers.Offset, jsonOffset:flatbuffers.Offset):flatbuffers.Offset {
+  DraftRequest.startDraftRequest(builder);
+  DraftRequest.addGameId(builder, gameIdOffset);
+  DraftRequest.addJson(builder, jsonOffset);
+  return DraftRequest.endDraftRequest(builder);
+}
+}

ui/src/gen/fbs/scrabblefb/draft-view.ts

@@ -0,0 +1,48 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import * as flatbuffers from 'flatbuffers';
+
+export class DraftView {
+  bb: flatbuffers.ByteBuffer|null = null;
+  bb_pos = 0;
+  __init(i:number, bb:flatbuffers.ByteBuffer):DraftView {
+  this.bb_pos = i;
+  this.bb = bb;
+  return this;
+}
+
+static getRootAsDraftView(bb:flatbuffers.ByteBuffer, obj?:DraftView):DraftView {
+  return (obj || new DraftView()).__init(bb.readInt32(bb.position()) + bb.position(), bb);
+}
+
+static getSizePrefixedRootAsDraftView(bb:flatbuffers.ByteBuffer, obj?:DraftView):DraftView {
+  bb.setPosition(bb.position() + flatbuffers.SIZE_PREFIX_LENGTH);
+  return (obj || new DraftView()).__init(bb.readInt32(bb.position()) + bb.position(), bb);
+}
+
+json():string|null
+json(optionalEncoding:flatbuffers.Encoding):string|Uint8Array|null
+json(optionalEncoding?:any):string|Uint8Array|null {
+  const offset = this.bb!.__offset(this.bb_pos, 4);
+  return offset ? this.bb!.__string(this.bb_pos + offset, optionalEncoding) : null;
+}
+
+static startDraftView(builder:flatbuffers.Builder) {
+  builder.startObject(1);
+}
+
+static addJson(builder:flatbuffers.Builder, jsonOffset:flatbuffers.Offset) {
+  builder.addFieldOffset(0, jsonOffset, 0);
+}
+
+static endDraftView(builder:flatbuffers.Builder):flatbuffers.Offset {
+  const offset = builder.endObject();
+  return offset;
+}
+
+static createDraftView(builder:flatbuffers.Builder, jsonOffset:flatbuffers.Offset):flatbuffers.Offset {
+  DraftView.startDraftView(builder);
+  DraftView.addJson(builder, jsonOffset);
+  return DraftView.endDraftView(builder);
+}
+}