refactor(domain): make FeedId circulate through the domain and repository

FeedId is now the type of Feed.id and of every single-feed method on
FeedRepository; callers wrap raw strings via FeedId.fromTrusted at the
repository boundary. String-medium operations (URLs, logs, JSON,
list registry, email keys) stay string. Drop the redundant
generateFeedId wrapper in favour of FeedId.generate.

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

src/routes/favicon.ts

@@ -1,6 +1,7 @@
 import { Context } from "hono";
 import { Env } from "../types";
 import { FeedRepository } from "../domain/feed-repository";
+import { FeedId } from "../domain/value-objects/feed-id";
 import { cacheFaviconForDomain, getCachedIcon } from "../utils/favicon-fetcher";
 
 export const FAVICON_PATH = "/favicon.svg";
@@ -40,7 +41,9 @@ export async function handleFeedFavicon(
   const feedId = c.req.param("feedId");
   if (!feedId) return projectFavicon();
 
-  const metadata = await FeedRepository.from(env).getMetadata(feedId);
+  const metadata = await FeedRepository.from(env).getMetadata(
+    FeedId.fromTrusted(feedId),
+  );
   const domain = metadata?.iconDomain;
   if (!domain) return projectFavicon();