fix(feed): use permalink URL as Atom entry id, strip mso-* inline styles

- Entry <id> was a non-URL string (timestamp + base64 snippet), which
  is invalid per the Atom spec; now uses the entry permalink URL which
  is both valid and stable across feed regeneration
- Strip mso-* properties from inline style attributes in extracted body
  content to eliminate the feed validator DangerousStyleAttr warning
  caused by Microsoft Office HTML in newsletter emails

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

src/utils/feed-generator.ts

@@ -17,11 +17,23 @@ function parseFromAddress(from: string): { name: string; email?: string } {
 // the body fragment in <description>/<content:encoded>, not a full document.
 export function extractBodyContent(html: string): string {
   const withClose = html.match(/<body[^>]*>([\s\S]*?)<\/body>/i);
-  if (withClose) return withClose[1];
-  // Some HTML emails omit </body>; capture everything after the opening tag
-  const withoutClose = html.match(/<body[^>]*>([\s\S]*)/i);
-  if (withoutClose) return withoutClose[1].replace(/<\/html>\s*$/i, "");
-  return html;
+  const body = withClose
+    ? withClose[1]
+    : (() => {
+        const withoutClose = html.match(/<body[^>]*>([\s\S]*)/i);
+        return withoutClose
+          ? withoutClose[1].replace(/<\/html>\s*$/i, "")
+          : html;
+      })();
+  // Strip mso-* properties from inline styles (Office HTML — triggers feed validator warnings)
+  return body.replace(/\bstyle="([^"]*)"/gi, (_match, style: string) => {
+    const cleaned = style
+      .split(";")
+      .map((p) => p.trim())
+      .filter((p) => p && !/^mso-/i.test(p))
+      .join("; ");
+    return cleaned ? `style="${cleaned}"` : "";
+  });
 }
 
 function buildFeed(
@@ -56,13 +68,13 @@ function buildFeed(
   });
 
   for (const email of emails) {
-    const uniqueId = `${email.receivedAt}-${Buffer.from(email.subject).toString("base64").substring(0, 10)}`;
+    const entryUrl = `${baseUrl}/entries/${feedId}/${email.receivedAt}`;
     const firstAttachment = email.attachments?.[0];
     const bodyContent = extractBodyContent(email.content);
     feed.addItem({
       title: email.subject,
-      id: uniqueId,
-      link: `${baseUrl}/entries/${feedId}/${email.receivedAt}`,
+      id: entryUrl,
+      link: entryUrl,
       description: bodyContent,
       content: bodyContent,
       author: [parseFromAddress(email.from)],