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/components/Timeline.tsx

@@ -1,6 +1,6 @@
 import { useEffect, useRef } from "react";
-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";
 import { DAY } from "../../shared/time.ts";
 import type { RowEvent } from "./EventRow.tsx";
 import { URGENCY_COLOR } from "./Meter.tsx";
@@ -42,6 +42,7 @@ export function Timeline({
    */
   isDone: (id: string) => boolean;
 }) {
+  const gameMeta = useGameMeta();
   const scroller = useRef<HTMLDivElement>(null);
 
   const ends = rows.map((r) => r.clock.endsMs ?? r.clock.startsMs + 14 * DAY);
@@ -75,7 +76,7 @@ export function Timeline({
     );
   }
 
-  const byGame = new Map<GameId, RowEvent[]>();
+  const byGame = new Map<LaneId, RowEvent[]>();
   for (const row of rows) {
     byGame.set(row.event.game, [...(byGame.get(row.event.game) ?? []), row]);
   }