feat: enhance blog and SEO features with new plugins and metadata

- Introduced rehypeLazyImages plugin for lazy loading images in blog posts.
- Updated sitemap integration to include last modified dates for blog posts.
- Enhanced Head and BaseLayout components to support additional Open Graph metadata.
- Improved RSS feed generation with sanitized content and author information.
- Updated manifest.json for a darker theme and standalone display mode.
- Added support for language-specific attributes in various components.
- Refactored blog post handling to include modified and published timestamps.

astro.config.mjs

@@ -1,17 +1,54 @@
 import { defineConfig } from "astro/config";
+import { globbySync } from "globby";
+import fs from "node:fs";
+import matter from "gray-matter";
+import path from "node:path";
+import rehypeExternalLinks from "rehype-external-links";
+import sitemap from "@astrojs/sitemap";
+
 import { remarkReadingTime } from "./src/plugins/remarkReadingTime";
 import ogImages from "./src/integrations/ogImages";
-import sitemap from "@astrojs/sitemap";
+import rehypeLazyImages from "./src/plugins/rehypeLazyImages";
+
+const blogDir = path.resolve("./src/content/blog");
+
+const lastmodBySlug = Object.fromEntries(
+	globbySync("*.md", { cwd: blogDir }).map((file) => {
+		const slug = file.replace(/\.md$/, "");
+		const { data } = matter(fs.readFileSync(path.join(blogDir, file), "utf8"));
+		const date = data.dateModified ?? data.datePublished;
+		return [slug, new Date(date).toISOString()];
+	})
+);
+
+const buildLastmod = new Date().toISOString();
 
 export default defineConfig({
 	site: "https://popov.link",
 	output: "static",
-	integrations: [sitemap(), ogImages()],
+	integrations: [
+		sitemap({
+			serialize(item) {
+				const url = new URL(item.url);
+				const match = url.pathname.match(/^\/blog\/([^/]+)\/?$/);
+
+				if (match && lastmodBySlug[match[1]]) {
+					item.lastmod = lastmodBySlug[match[1]];
+				} else {
+					item.lastmod = buildLastmod;
+				}
+
+				return item;
+			},
+		}),
+		ogImages(),
+	],
 	build: {
 		inlineStylesheets: "always",
 	},
 	markdown: {
 		remarkPlugins: [remarkReadingTime],
+		rehypePlugins: [[rehypeExternalLinks, { target: "_blank", rel: ["noopener", "noreferrer"] }], rehypeLazyImages],
 		shikiConfig: {
 			theme: "vitesse-dark",
 		},