Save state for every game between sessions

A game against the computer is kept as it is played (the host's true state plus its
table config, one file per game) and can be resumed from the main menu or the game's
setup screen. Leaving keeps the position; End game discards it; a finished game is
not kept; a networked table is not saved.

MatchController gains restore() and an onHostState listener; MatchSaver writes off
the main thread and flushes on leaving and ON_STOP. Tests cover the store, the saver,
resuming, and a save/resume round trip of every game in the catalogue at every move.

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_016eTor2tpxKb4dXbd8RqnvZ

docs/README.md

@@ -42,6 +42,8 @@ Naming: the catalogue id, lowercase, e.g. `crazy8s` → `RULES-crazy8s.md`.
 
 - Build, CI, releases and OTA are described in the CI section of the root
   [README](../README.md).
+- [SAVED-GAMES.md](SAVED-GAMES.md) — how a game in progress is kept between sessions, and what is
+  not kept.
 - [UI-catan.md](UI-catan.md) — how the Katan screen is layered, and how to restyle,
   re-copy or re-lay-out it without touching the rules.
 - `licenses/` — third-party licences that must travel with the app