feat: add shared time, games and feed contracts

Time is this product's subject, so the vocabulary lives in one module:
remaining, progress through a window, and urgency. Urgency is derived from
absolute time left, deliberately independent of proportion — a 90-day event
with three hours left is as urgent as a 3-day one.

An unannounced end is never urgent and has no progress: "we don't know" and
"loads of time" are different facts, and conflating them is what this
product exists to avoid.

Games carry a hue for identity only. Urgency is a separate axis, so one
glance answers both "whose event is this?" and "how long have I got?".

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

src/shared/feed.ts

@@ -0,0 +1,29 @@
+import { z } from "zod";
+import { GachaEvent, GameId } from "./schema.ts";
+
+/**
+ * The wire contract between server and client.
+ *
+ * The client refuses a `schemaVersion` it does not know rather than guessing at
+ * unfamiliar fields. Additive fields do not bump it; removing or retyping one
+ * does. See docs/DATA-MODEL.md § Schema versioning.
+ */
+export const SCHEMA_VERSION = 1;
+
+export const SourceHealth = z.object({
+  sourceId: z.string(),
+  game: GameId,
+  url: z.string().url(),
+  lastSuccessAt: z.string().datetime().nullable(),
+  eventCount: z.number().int().nonnegative(),
+});
+
+export const EventFeed = z.object({
+  schemaVersion: z.literal(SCHEMA_VERSION),
+  generatedAt: z.string().datetime(),
+  events: z.array(GachaEvent),
+  sources: z.array(SourceHealth),
+});
+
+export type SourceHealth = z.infer<typeof SourceHealth>;
+export type EventFeed = z.infer<typeof EventFeed>;