feat(blog): add blog section and rss feed

- Add blog content collection schema and welcome post
- Create blog index, post layout components, and dynamic routing
- Add `@astrojs/rss` dependency and implement RSS feed generation
- Add blog links to header and footer navigation
- Update changelog with Gemini 3.1 Pro enhancement notes

src/content/blog/welcome.md

@@ -0,0 +1,21 @@
+---
+title: "Welcome to the Zaguán Blade Blog"
+description: "Announcing our new blog where we'll share updates, tutorials, and insights about AI-powered development."
+pubDate: 2026-02-22
+tags: ["announcement"]
+categories: ["General"]
+draft: true
+---
+
+# Welcome to the Zaguán Blade Blog
+
+This is a placeholder post. Replace me with your actual blog content!
+
+## What's Coming
+
+- Release announcements and changelogs
+- Tutorials and how-to guides
+- Tips and tricks for getting the most out of Zaguán Blade
+- Insights into AI-powered development
+
+Stay tuned for more!