feat: complete Phase 2 tech debt remediation

- Extract shared RSS/Atom fetch logic into feed-fetcher utility (P1-3)
- Split email-processor into validateEmail/storeEmail functions (P1-6)
- Add stateless HMAC-SHA256 CSRF protection to admin forms (P2-8)
- Fix Hono<{ Bindings: Env }> type safety across all routes (P3-13)
- Add entries.test.ts and files.test.ts with full coverage (P1-7)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/routes/atom.ts

@@ -1,56 +1,27 @@
 import { Context } from "hono";
-import { Env, FeedConfig, FeedMetadata, EmailData } from "../types";
+import { Env } from "../types";
 import { generateAtomFeed } from "../utils/feed-generator";
+import { fetchFeedData } from "../utils/feed-fetcher";
 
-export async function handle(c: Context): Promise<Response> {
+export async function handle(c: Context<{ Bindings: Env }>): Promise<Response> {
   try {
-    const env = c.env as unknown as Env;
-
     const feedId = c.req.param("feedId");
-
     if (!feedId) {
       return new Response("Feed ID is required", { status: 400 });
     }
 
-    const emailStorage = env.EMAIL_STORAGE;
-
-    const feedMetadata = (await emailStorage.get(
-      `feed:${feedId}:metadata`,
-      "json",
-    )) as FeedMetadata | null;
-
-    if (!feedMetadata) {
+    const feedData = await fetchFeedData(feedId, c.env, "atom");
+    if (!feedData) {
       return new Response("Feed not found", { status: 404 });
     }
 
-    const feedConfig = ((await emailStorage.get(
-      `feed:${feedId}:config`,
-      "json",
-    )) as FeedConfig | null) || {
-      title: `Newsletter Feed ${feedId}`,
-      description: "Converted email newsletter",
-      site_url: `https://${env.DOMAIN}/atom/${feedId}`,
-      feed_url: `https://${env.DOMAIN}/atom/${feedId}`,
-      language: "en",
-      created_at: Date.now(),
-    };
-
-    const emails = feedMetadata.emails.slice(0, 20);
-    const emailsData: EmailData[] = [];
-
-    for (const email of emails) {
-      const emailData = (await emailStorage.get(
-        email.key,
-        "json",
-      )) as EmailData | null;
-      if (emailData) {
-        emailsData.push(emailData);
-      }
-    }
-
-    const baseUrl = `https://${env.DOMAIN}`;
-    const atomXml = generateAtomFeed(feedConfig, emailsData, baseUrl, feedId);
-
+    const baseUrl = `https://${c.env.DOMAIN}`;
+    const atomXml = generateAtomFeed(
+      feedData.feedConfig,
+      feedData.emails,
+      baseUrl,
+      feedId,
+    );
     const linkHeader = [
       `<${baseUrl}/hub>; rel="hub"`,
       `<${baseUrl}/atom/${feedId}>; rel="self"`,