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) <noreply@anthropic.com>

src/client/components/NextUp.tsx

@@ -12,6 +12,7 @@ import { Meter, URGENCY_COLOR } from "./Meter.tsx";
  */
 export function NextUp({
   row,
+  focused,
   onOpen,
 }: {
   /**
@@ -21,6 +22,8 @@ export function NextUp({
    * they have chosen to keep it elsewhere.
    */
   row: RowEvent | null;
+  /** Name of the game being focused on, when the page is narrowed to one. */
+  focused: string | null;
   onOpen: (id: string) => void;
 }) {
   if (row === null) {
@@ -28,8 +31,9 @@ export function NextUp({
       <section className="border-b border-hairline px-4 py-8">
         <p className="eyebrow">Nothing running</p>
         <p className="mt-2 max-w-sm text-sm text-muted">
-          Nothing live and unfinished in the games you have switched on. Turn a
-          game back on below, or check again after the next patch.
+          {focused === null
+            ? "Nothing live and unfinished in the games you have switched on. Turn a game back on below, or check again after the next patch."
+            : `Nothing live and unfinished in ${focused}. Move to the next game, or show all of them.`}
         </p>
       </section>
     );