Set site and base in Astro config

Add site and base fields to docs/astro.config.mjs to configure deployment target and base path for GitHub Pages. Sets site to https://gdcc.github.io and base to /pyDataverse so generated URLs resolve correctly when hosted under that path.

Author: JR-1991

docs/astro.config.mjs

@@ -8,6 +8,8 @@ import mermaid from 'astro-mermaid';
 
 // https://astro.build/config
 export default defineConfig({
+	site: 'https://gdcc.github.io',
+	base: '/pyDataverse',
 	redirects: {
 		'/': '/getting-started',
 	},