make base.njk default template, update index

eleventy.config.js

@@ -10,6 +10,8 @@ export default function (eleventyConfig) {
 
     eleventyConfig.addFilter("readableDate", (date) => UTC_LONG.format(date));
     eleventyConfig.addFilter("isoDate", (date) => date.toISOString().slice(0, 10));
+    
+    eleventyConfig.addGlobalData("layout", "layouts/base.njk");
 
     return {
         dir: { input: "src" },