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/admin.tsx

@@ -9,7 +9,7 @@ import { logger } from "../infrastructure/logger";
 import { timingSafeEqual, checkProxyAuth } from "../infrastructure/auth";
 import { Layout, clampText } from "./admin/ui";
 import { FeedRepository } from "../infrastructure/feed-repository";
-import { renameFeed } from "../application/feed-service";
+import { editFeedDetails } from "../application/feed-service";
 import {
   feedRssUrl,
   feedAtomUrl,
@@ -997,7 +997,7 @@ app.post(
       const { title, description } = c.req.valid("json");
 
       // In-place edit: only title/description, expiry untouched.
-      const result = await renameFeed(env, feedId, { title, description });
+      const result = await editFeedDetails(env, feedId, { title, description });
 
       if (result.status === "not_found") {
         return c.json({ error: "Feed not found" }, 404);