refactor(domain): split Icon/WebSub/Counters out of FeedRepository

FeedRepository no longer owns favicons, WebSub subscriber lists or the
monitoring counters singleton. Each concern gets its own repository
(IconRepository, WebSubSubscriptionRepository, CountersRepository),
sharing the key schema via feed-keys. KV key strings are unchanged;
counters increment policy stays in utils/stats.ts.

Co-Authored-By: Claude Opus 4.7 <[email protected]>

src/utils/websub.ts

@@ -2,12 +2,13 @@ import { Env, FeedConfig, EmailData, WebSubSubscription } from "../types";
 import { generateRssFeed, generateAtomFeed } from "./feed-generator";
 import { baseUrl, feedRssUrl, feedAtomUrl, feedUrl } from "./urls";
 import { FeedRepository } from "../domain/feed-repository";
+import { WebSubSubscriptionRepository } from "../domain/websub-subscription-repository";
 
 export async function getSubscriptions(
   feedId: string,
   env: Env,
 ): Promise<WebSubSubscription[]> {
-  return FeedRepository.from(env).getSubscriptions(feedId);
+  return WebSubSubscriptionRepository.from(env).get(feedId);
 }
 
 export async function saveSubscriptions(
@@ -15,7 +16,7 @@ export async function saveSubscriptions(
   subscriptions: WebSubSubscription[],
   env: Env,
 ): Promise<void> {
-  await FeedRepository.from(env).saveSubscriptions(feedId, subscriptions);
+  await WebSubSubscriptionRepository.from(env).save(feedId, subscriptions);
 }
 
 export async function buildHmacSignature(