refactor(domain): split updateFeedRecord into renameFeed and editFeed

The inPlace boolean hid two distinct intentions. Replace it with two
intention-revealing operations backed by Feed.rename (presentational,
never touches expiry) and Feed.edit (full edit, recomputes expiry,
rejects expired). Add FeedRepository.saveConfig so these config-only
edits don't re-write (and risk clobbering) the email index.

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

src/routes/admin/feeds.tsx

@@ -12,7 +12,7 @@ import { purgeFeedKeysStep, collectUnsubscribeUrls } from "./helpers";
 import { FeedRepository } from "../../domain/feed-repository";
 import {
   createFeedRecord,
-  updateFeedRecord,
+  editFeed,
   deleteFeedRecord,
   deleteFeedFastDetailed,
 } from "../../lib/feed-service";
@@ -329,7 +329,7 @@ feedsRouter.post("/:feedId/edit", async (c) => {
       blockedSenders,
     });
 
-    const result = await updateFeedRecord(env, feedId, {
+    const result = await editFeed(env, feedId, {
       title: parsedData.title,
       description: parsedData.description,
       language: parsedData.language,