Enhance configuration and layout: add environment variables, improve metadata, and update content section keys for consistency

Co-authored-by: Copilot <copilot@github.com>

astro.config.mjs

@@ -1,14 +1,19 @@
 // @ts-check
 import { defineConfig } from 'astro/config';
 import tailwindcss from '@tailwindcss/vite';
+import { loadEnv } from 'vite';
 
 import mdx from '@astrojs/mdx';
 
+const env = loadEnv(process.env.NODE_ENV ?? 'development', process.cwd(), 'PUBLIC_');
+
 // https://astro.build/config
 export default defineConfig({
+  site: env.PUBLIC_SITE_URL,
+
   vite: {
     plugins: [tailwindcss()]
   },
 
   integrations: [mdx()]
-});
+});