refactor: split src into domain / application / infrastructure layers

Replace the history-driven lib/ + utils/ split with DDD layers:
- domain/: aggregate, repositories, value objects, pure parsers/format
- application/: feed-service, email-processor, feed-fetcher, stats
- infrastructure/: logging, auth, KV/R2 adapters, HTTP, framework glue

Pure file relocation; imports updated mechanically. Behaviour unchanged.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/infrastructure/urls.ts

@@ -0,0 +1,30 @@
+import { Env } from "../types";
+
+export function baseUrl(env: Env): string {
+  return `https://${env.DOMAIN}`;
+}
+
+export function feedRssUrl(feedId: string, env: Env): string {
+  return `${baseUrl(env)}/rss/${feedId}`;
+}
+
+export function feedAtomUrl(feedId: string, env: Env): string {
+  return `${baseUrl(env)}/atom/${feedId}`;
+}
+
+export function feedUrl(
+  format: "rss" | "atom",
+  feedId: string,
+  env: Env,
+): string {
+  return format === "rss" ? feedRssUrl(feedId, env) : feedAtomUrl(feedId, env);
+}
+
+export function feedEmailAddress(feedId: string, env: Env): string {
+  return `${feedId}@${env.EMAIL_DOMAIN ?? env.DOMAIN}`;
+}
+
+export function feedTopicPattern(env: Env): RegExp {
+  const escaped = env.DOMAIN.replaceAll(".", "\\.");
+  return new RegExp(`^https://${escaped}/(rss|atom)/([^/]+)$`);
+}