feat: enhance SEO with sitemap and robots.txt, add Open Graph and Twitter meta tags

.eleventy.js

@@ -6,6 +6,9 @@ module.exports = function(eleventyConfig) {
   eleventyConfig.addPassthroughCopy("src/resume");
   eleventyConfig.addPassthroughCopy("src/assets/images");
   eleventyConfig.addPassthroughCopy({ "favicon" : "/" } );
+  eleventyConfig.addPassthroughCopy({ 'src/robots.txt': '/robots.txt' });
+  eleventyConfig.addPassthroughCopy({ 'src/sitemap.xml': '/sitemap.xml' });
+
   // Add a filter for readable dates using vanilla JS
   eleventyConfig.addFilter("readableDate", dateObj => {
     // The toLocaleDateString method can be used to format dates
@@ -19,6 +22,14 @@ module.exports = function(eleventyConfig) {
     });
   });
 
+  // Add htmlDateString filter for sitemap <lastmod>
+  eleventyConfig.addFilter("htmlDateString", dateObj => {
+    if (!dateObj) return "";
+    // Format date as YYYY-MM-DD for sitemaps
+    const d = new Date(dateObj);
+    return d.toISOString().split("T")[0];
+  });
+
   // Shortcode for creating a callout box
   // This is a "paired shortcode" which means it has a start and end tag.
   eleventyConfig.addPairedShortcode("callout", function(content, title) {