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/routes/admin.tsx

@@ -5,12 +5,16 @@ import { z } from "zod";
 import { Env } from "../types";
 import { csrf } from "hono/csrf";
 import { ADMIN_COOKIE_MAX_AGE } from "../config/constants";
-import { logger } from "../lib/logger";
-import { timingSafeEqual, checkProxyAuth } from "../lib/auth";
+import { logger } from "../infrastructure/logger";
+import { timingSafeEqual, checkProxyAuth } from "../infrastructure/auth";
 import { Layout, clampText } from "./admin/ui";
 import { FeedRepository } from "../domain/feed-repository";
-import { renameFeed } from "../lib/feed-service";
-import { feedRssUrl, feedAtomUrl, feedEmailAddress } from "../utils/urls";
+import { renameFeed } from "../application/feed-service";
+import {
+  feedRssUrl,
+  feedAtomUrl,
+  feedEmailAddress,
+} from "../infrastructure/urls";
 import { feedsRouter } from "./admin/feeds";
 import { emailsRouter } from "./admin/emails";
 import { dashboardScript } from "../scripts/generated/dashboard";