feat(feed): optional per-feed sender-in-title toggle

Add a per-feed senderInTitle flag (domain FeedState.senderInTitle ↔
FeedConfig.sender_in_title). When set, the feed generator prefixes each
entry title with [Sender] (display name, falling back to the address).
Exposed as an admin edit-form checkbox and across the REST API
create/update/response schemas.

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

src/infrastructure/feed-generator.ts

@@ -74,8 +74,12 @@ function buildFeed(
       baseUrl,
       EmailAddress.parse(email.from)?.siteBaseUrl() ?? "",
     );
+    const subject = htmlToText(email.subject);
+    const title = feedConfig.sender_in_title
+      ? `[${parseFromAddress(email.from).name ?? email.from}] ${subject}`
+      : subject;
     feed.addItem({
-      title: htmlToText(email.subject),
+      title,
       id: entryUrl,
       link: entryUrl,
       description: bodyContent,