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/lib/transport.ts

@@ -114,6 +114,12 @@ export function createTransport(baseUrl: string): GatewayClient {
     async complaint(id, word, note) {
       await exec('game.complaint', codec.encodeComplaint(id, word, note));
     },
+    async draftGet(id) {
+      return codec.decodeDraftView(await exec('draft.get', codec.encodeGameAction(id)));
+    },
+    async draftSave(id, json) {
+      await exec('draft.save', codec.encodeDraftSave(id, json));
+    },
 
     async chatPost(id, body) {
       return codec.decodeChatMessage(await exec('chat.post', codec.encodeChatPost(id, body)));