feat(offline): offline lobby lists + creates local vs_ai games

In offline mode the lobby now shows only the device-local games and its
New-vs-AI entry creates one through the in-browser engine — the visible
payoff of the offline mode.

- LocalSource.list() reconstructs a lobby GameView per stored local game by
  replay, exposed through the lazy gamesource proxy; unit-tested via an
  in-memory store.
- Lobby.load() branches on offlineMode: lists local games and skips every
  gateway call (no online games/invitations/incoming); the Stats tab is
  disabled offline.
- NewGame offline: find() creates a device-local vs_ai game via
  LocalSource.create using the profile's advertised dict version + a local
  seed; the friends flow and the random-opponent option are hidden, and the
  variant picker / Start are enabled offline (were gated on connection).
- id.ts: newLocalGameId + randomSeed (tested).

Docs: ARCHITECTURE + FUNCTIONAL(+ru) offline-mode section.

Deferred to fast-follow: the Settings Friends/Profile/Feedback affordance
gating, the flip-to-offline readiness wait, the offline mock e2e (needs
mock-dawg support), and the local-hint UI. The offline flow is verified on
the test contour — the mock e2e cannot enter offline mode (the toggle is
gated to an installed PWA).

ui/src/lib/gamesource.ts

@@ -39,6 +39,7 @@ export const localSource = {
   draftGet: (_id) => load().then((s) => s.draftGet()),
   draftSave: (_id, _json) => load().then((s) => s.draftSave()),
   create: (opts) => load().then((s) => s.create(opts)),
+  list: () => load().then((s) => s.list()),
   // events must return the unsubscribe synchronously (the screen subscribes in onMount), so it wires
   // the real subscription once the engine loads and, until then, cancels a pending subscribe.
   events: (id, onEvent) => {
@@ -52,7 +53,7 @@ export const localSource = {
       unsub();
     };
   },
-} satisfies GameLoopSource & Pick<LocalSource, 'events' | 'create'>;
+} satisfies GameLoopSource & Pick<LocalSource, 'events' | 'create' | 'list'>;
 
 /**
  * gameSource returns the source that runs the game with the given id: the local engine for a local