Two documents catch up with the save rule

The quickstart's bug-reporting section told a player to save the game and send the file;
in a Competitive multiplayer game that button now waits for the end, so it says so and says
to note the Day and Stage instead. The route table in multiplayer.md gains `/api/save`,
which had been in the code since 0.8.0.10 and never in the table. No code, no version.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FrCWubm9GAftYCm2hWdKwK

docs/architecture/multiplayer.md

@@ -245,6 +245,7 @@ special handling: `pump` stops, and the next push simply carries a `Menu` contai
 POST /api/lobby/create, /api/lobby/join      lobby
 POST /api/intent          { gameId, seq, intent }
 GET  /api/stream          EventSource — per-seat frames, with Last-Event-ID resume
+GET  /api/save            ?token= — the seat's own save; 403 SAVE_AFTER_FINISH in a running Competitive game
 GET  /api/health          { ok, service, engineVersion, games } — unauthenticated; see below
 GET  /api/games           every game and lobby, summarised          ┐
 GET  /api/games/<id>/save the save, for keeping or replaying        ├ ADMIN_SECRET