feat(custom): model reader-authored games and events

The data layer for PRD F13, with no UI and no behaviour change yet.

src/shared/custom.ts defines the two key spaces, their schemas, and the
projection into what the views read. Two properties are the point of it:

- A reader's event id is random, not derived from their title. They can type a
  scraped event's exact name and date, which under ${game}:${slug}:${date} is a
  byte-identical key — one completion mark and one streak silently shared by two
  events. Randomness also means renaming their own event never moves its id.
- A reader's event carries no sourceUrl, so a hand-entered date can never be
  attributed to a source, and claims no region split, because they entered one
  instant and inventing three would fabricate two of them.

The rest is widening what was GameId-shaped into a lane that may be one of
theirs: clockFor takes the boundary fields structurally so their events run on
the identical countdown rather than a second one, day keys fall back to the
regional default for a lane with no server map, and gameMeta becomes a context
resolver so metaFor stays pure and total — a lane can outlive its game when an
import carries an event whose game did not come with it.

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

src/client/App.tsx

@@ -26,8 +26,8 @@ import {
 } from "./state/lens.ts";
 import { clockFor, DAY, formatRemaining } from "../shared/time.ts";
 import { dailySummary, isDaily, resolveDaily } from "../shared/daily.ts";
-import { gameMeta } from "../shared/games.ts";
-import type { GameId } from "../shared/schema.ts";
+import { useGameMeta } from "./state/gameMeta.tsx";
+import type { LaneId } from "../shared/custom.ts";
 
 type View = "soon" | "calendar";
 
@@ -70,6 +70,7 @@ export function App() {
   // The event most recently ignored, so it can be put back without hunting for
   // a row that just disappeared.
   const [lastIgnored, setLastIgnored] = useState<{ id: string; title: string } | null>(null);
+  const gameMeta = useGameMeta();
   const now = useNow();
   const online = useOnline();
   const { prefs, update, toggleGame } = usePrefs();
@@ -151,7 +152,7 @@ export function App() {
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [state, prefs.region, Math.floor(now / 60_000)]);
 
-  const games = useMemo<GameId[]>(
+  const games = useMemo<LaneId[]>(
     () => [...new Set(allRows.map((r) => r.event.game))],
     [allRows],
   );