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]>

docs/ARCHITECTURE.md

@@ -88,9 +88,10 @@ src/
       Timeline.tsx      calendar lanes              (F1)
       EventDetail.tsx   detail sheet, ignore action (F9)
       ProgressControls  status, effort, note        (F12)
-      Dailies.tsx       today's strip of repeating jobs
+      Dailies.tsx       today's strip, per-game reset clocks
       DailyChecklist    one repeating event's whole run
       Fireworks.tsx     the burst when the last daily lands
+      GameFocus.tsx     one game at a time          (F4a)
       Controls.tsx      games, region, export/import(F4, F5, F6)
       Welcome.tsx       first-run game picker       (F8)
       Toast.tsx         undo an ignore
@@ -100,9 +101,9 @@ src/
       useMarkSet.ts     ignores (and the superseded completions shape)
       useProgress.ts    status, effort, note, daily override  (F12)
       useDailyLog.ts    which game-days are ticked off
-      usePrefs.ts       region, filters, onboarding flags
+      usePrefs.ts       region, filters, focus, onboarding flags
       sort.ts           deadline order, or what you're partway through
-      lens.ts           who sees which rows — outstanding, next-to-expire
+      lens.ts           who sees which rows — focus, outstanding, next-to-expire
 serve.ts                static server + /api/health              ✓ built
 scripts/
   build-feed.ts         fixtures → public/data/events.v1.json     ✓ built