Add blog post and support pubDate/tags

Add new post "After the Silence". Update content schema to use
pubDate and include tags (default empty). Update blog listing,
post page and start page to use pubDate, render tag lists, and
compute/show up to two related posts by tag overlap. Misc
formatting and small display tweaks.

src/content/blog/hello-world.md

@@ -1,7 +1,8 @@
----
+---
 title: "Welcome to the Den"
-date: 2026-03-01
 description: "First proper post. Why I built this site, what it runs on, and what to expect."
+pubDate: 2026-03-01
+tags: ["self-hosting", "privacy", "personal-web", "infrastructure"]
 draft: false
 ---
 
@@ -11,7 +12,7 @@ So I finally got around to setting up a proper blog. Welcome.
 
 I wanted a place to write that wasn't owned by a corporation. No Medium, no Substack, no algorithm deciding who sees what. Just markdown files on my own server, served by nginx from a Docker container I control.
 
-That's the whole point of the den — owning your own space on the internet.
+That's the whole point of the den - owning your own space on the internet.
 
 ## What It Runs On