feat(wpcarro/blog): Add a blog index page

TL;DR:
- Create an index page to list blog posts
- Drop blog.wpcarro.dev -> wpcarro.dev/blog
- Create fragments directory to host reusable static website components
- Consume fragments in wpcarro.dev and wpcarro.dev/blog for brand consistency

Change-Id: Ib8440300c008c3c0c5e5a6f207e4ea207dd41b47
Reviewed-on: https://cl.tvl.fyi/c/depot/+/4717
Tested-by: BuildkiteCI
Reviewed-by: wpcarro <wpcarro@gmail.com>
Autosubmit: wpcarro <wpcarro@gmail.com>

users/wpcarro/website/fragments/addendum.html

@@ -0,0 +1,13 @@
+    </div>
+    <script>
+      const $header = document.querySelector("header");
+      const dropShadow = "drop-shadow-md";
+      const update = () => window.scrollY !== 0 ?
+        $header.classList.add(dropShadow) :
+        $header.classList.remove(dropShadow);
+
+      update();
+      document.addEventListener("scroll", update);
+    </script>
+  </body>
+</html>