feat(filter): focus one game at a time

Switching games on and off says which games you play, and is set once.
It's the wrong tool for what a player of four games does while reading —
clear one game, move to the next — which cost two taps per game and left
the settings panel no longer describing what they play.

Focus is a lens over that filter, not a second filter: a bar at the top,
above everything it narrows, with a "next game" control that steps
through and ends by returning to all. It never touches hiddenGames, and
a focus on a game since switched off is ignored rather than obeyed, so
it can't strand you on a blank page whose cause is elsewhere. Each chip
carries that game's outstanding count, so a game with nothing waiting
says so before you visit it.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

CLAUDE.md

@@ -81,9 +81,10 @@ src/ingest/       html.ts, dates.ts (six formats), merge.ts, sanitize.ts, robots
   adapters/       index.ts — SOURCES registry binding url+game+parser, and the sanitize seam
 src/client/       React app, service worker, manifest
   state/          progress, daily log, ignores, prefs, sort — all localStorage
+                  lens.ts — who sees which rows (focus, outstanding, next-to-expire); pure
 scripts/          build-feed.ts, parse-fixture.ts (offline), refresh-sources.ts (fetches)
 serve.ts          static server + /api/health
-test/             309 tests
+test/             318 tests
 fixtures/<game>/  raw HTML + .expected.json per source — pinned, kept forever
 snapshots/        current page per source, rewritten by refresh — see its README
 ```