feat(rss): include cover images as enclosures

Use getPostImage to resolve cover images for each post and include
them as RSS enclosure elements. Falls back to default cover if no
custom cover.png exists.

Author: CalvinAllen

src/pages/rss.xml.ts

@@ -3,6 +3,7 @@ import { getCollection } from 'astro:content';
 import type { APIContext } from 'astro';
 import sanitizeHtml from 'sanitize-html';
 import MarkdownIt from 'markdown-it';
+import { getPostImage } from '../lib/posts';
 
 const parser = new MarkdownIt();
 
@@ -49,13 +50,12 @@ export async function GET(context: APIContext) {
         }),
       };
 
-      if (post.data.image) {
-        item.enclosure = {
-          url: `${site}${post.data.image.src}`,
-          type: getMimeType(post.data.image.src),
-          length: 0,
-        };
-      }
+      const image = getPostImage(post);
+      item.enclosure = {
+        url: `${site}${image.src}`,
+        type: getMimeType(image.src),
+        length: 0,
+      };
 
       // Add custom data for bluesky post ID if present
       if (post.data.blueskyPostId) {