refactor: invert application↔routes boundary (Track B — points 3, 6a)

- Point 3: move the feed/email storage-cleanup helpers (purgeFeedKeysStep,
  collectUnsubscribeUrls, purgeExpiredFeeds, deleteKeysWithConcurrency,
  deleteAttachmentsForEmails) out of routes/admin/helpers.ts into
  src/application/feed-cleanup.ts, so the application layer no longer imports
  from routes/. deleteFeedRecord no longer takes a Hono Context: it accepts a
  BackgroundScheduler ((task) => void) and the HTTP edge passes
  (p) => waitUntilSafe(c, p). Application/domain are now Hono-Context-free.
- Point 6a: rename the misleadingly-named Feed.rename → Feed.editDetails (it
  edits title + description), and feed-service.renameFeed → editFeedDetails.

CLAUDE.md source layout updated. 351 tests pass; tsc --noEmit clean.

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

src/routes/api/index.ts

@@ -8,7 +8,8 @@ import {
   editFeed,
   deleteFeedRecord,
 } from "../../application/feed-service";
-import { deleteAttachmentsForEmails } from "../admin/helpers";
+import { deleteAttachmentsForEmails } from "../../application/feed-cleanup";
+import { waitUntilSafe } from "../../infrastructure/worker";
 import { FeedRepository } from "../../infrastructure/feed-repository";
 import { FeedId } from "../../domain/value-objects/feed-id";
 import { getStats } from "../../application/stats";
@@ -248,7 +249,9 @@ apiApp.openapi(
   async (c) => {
     const env = c.env;
     const { feedId } = c.req.valid("param");
-    const removed = await deleteFeedRecord(c, env, feedId);
+    const removed = await deleteFeedRecord(env, feedId, (p) =>
+      waitUntilSafe(c, p),
+    );
     if (!removed) return c.json({ error: "Feed not found" }, 404);
     return c.json({ ok: true }, 200);
   },