feat(lolschedule): per-chat subscribe/unsubscribe for the daily cron

Replaces the single LOLSCHEDULE_CHAT_ID env var with a KV-backed
subscriber list. New commands /lolschedule_subscribe and
/lolschedule_unsubscribe let each chat opt in/out. The cron now fans
out to every subscriber via Promise.allSettled so one blocked chat
cannot break the others.

tests/modules/lolschedule/subscribers.test.js

@@ -0,0 +1,43 @@
+import { beforeEach, describe, expect, it } from "vitest";
+import { createStore } from "../../../src/db/create-store.js";
+import {
+  addSubscriber,
+  listSubscribers,
+  removeSubscriber,
+} from "../../../src/modules/lolschedule/subscribers.js";
+import { makeFakeKv } from "../../fakes/fake-kv-namespace.js";
+
+describe("subscribers", () => {
+  let db;
+  beforeEach(() => {
+    db = createStore("lolschedule", { KV: makeFakeKv() });
+  });
+
+  it("starts empty", async () => {
+    expect(await listSubscribers(db)).toEqual([]);
+  });
+
+  it("adds a new subscriber and returns true", async () => {
+    expect(await addSubscriber(db, 42)).toBe(true);
+    expect(await listSubscribers(db)).toEqual([42]);
+  });
+
+  it("add is idempotent for an already-subscribed chat", async () => {
+    await addSubscriber(db, 42);
+    expect(await addSubscriber(db, 42)).toBe(false);
+    expect(await listSubscribers(db)).toEqual([42]);
+  });
+
+  it("removes an existing subscriber and returns true", async () => {
+    await addSubscriber(db, 1);
+    await addSubscriber(db, 2);
+    expect(await removeSubscriber(db, 1)).toBe(true);
+    expect(await listSubscribers(db)).toEqual([2]);
+  });
+
+  it("remove on a non-subscriber returns false and is a no-op", async () => {
+    await addSubscriber(db, 1);
+    expect(await removeSubscriber(db, 99)).toBe(false);
+    expect(await listSubscribers(db)).toEqual([1]);
+  });
+});