feat: enhance accessibility and language support across components

- Updated various components to include `lang` attributes for improved accessibility and SEO.
- Introduced a new `env.d.ts` file to define environment variables for better type safety.
- Adjusted the print width in `.prettierrc.mjs` for improved code formatting.
- Streamlined the `Header`, `PostElement`, and `SocialLinks` components for better structure and clarity.
- Added language support to blog posts and updated the layout to reflect these changes.

src/pages/feed.xml.js

@@ -10,7 +10,7 @@ export async function GET(context) {
 	});
 
 	return rss({
-		customData: `<language>ru-ru</language>`,
+		customData: `<language>en</language>`,
 		description: description,
 		items: posts.map((post) => ({
 			customData: post.data.customData,