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/pages/blog/[slug].astro

@@ -0,0 +1,19 @@
+---
+import { getCollection } from 'astro:content';
+import BlogPost from '../../layouts/BlogPost.astro';
+
+export async function getStaticPaths() {
+  const posts = await getCollection('blog');
+  return posts.map((post) => ({
+    params: { slug: post.slug },
+    props: post,
+  }));
+}
+
+const post = Astro.props;
+const { Content } = await post.render();
+---
+
+<BlogPost post={post}>
+  <Content />
+</BlogPost>