docs: add changelog entries for v1.33.1 through v1.37.0

Add missing changelog entries to content/pages/changelog-page.md:

v1.34.0 (2025-12-26): Blog page featured layout with hero post
- blogFeatured frontmatter field for posts
- Hero card displays first featured post with landscape image
- 2-column featured row for remaining featured posts
- 3-column grid for regular posts

v1.35.0 (2025-12-26): Image support at top of posts and pages
- showImageAtTop frontmatter field
- Full-width image display above post header
- Works for both posts and pages

v1.36.0 (2025-12-27): Social footer component
- Customizable social links (8 platform types)
- Copyright with auto-updating year
- showSocialFooter frontmatter field for per-page control
- Configurable via siteConfig.socialFooter

v1.37.0 (2025-12-27): Newsletter Admin UI
- Three-column admin interface at /newsletter-admin
- Subscriber management with search and filters
- Send newsletter panel (post selection or custom email)
- Weekly digest automation (Sunday 9am UTC)
- Developer notifications (subscriber alerts, weekly stats)
- Markdown-to-HTML conversion for custom emails

fork-config.json.example

@@ -55,6 +55,32 @@
     "type": "default",
     "slug": null,
     "originalHomeRoute": "/home"
+  },
+  "newsletter": {
+    "enabled": false,
+    "agentmail": {
+      "inbox": "newsletter@mail.agentmail.to"
+    },
+    "signup": {
+      "home": {
+        "enabled": false,
+        "position": "above-footer",
+        "title": "Stay Updated",
+        "description": "Get new posts delivered to your inbox."
+      },
+      "blogPage": {
+        "enabled": false,
+        "position": "above-footer",
+        "title": "Subscribe",
+        "description": "Get notified when new posts are published."
+      },
+      "posts": {
+        "enabled": false,
+        "position": "below-content",
+        "title": "Enjoyed this post?",
+        "description": "Subscribe for more updates."
+      }
+    }
   }
 }