docs: add brazilian portuguese I18n

Config Astro for new language pt-BR. Translate homepage, getting started,
resolve challenge and injection token challenge MDX files.

docs/astro.config.mjs

@@ -4,6 +4,7 @@ import { defineConfig } from 'astro/config';
 export const locales = {
   root: { label: 'English', lang: 'en' },
   es: { label: 'Español', lang: 'es' },
+  'pt-br': { label: 'Português (Brasil)', lang: 'pt-BR' },
 };
 
 // https://astro.build/config
@@ -28,6 +29,7 @@ export default defineConfig({
           autogenerate: { directory: 'guides' },
           translations: {
             es: 'Guías',
+            'pt-BR': 'Guias',
           },
         },
         {
@@ -35,6 +37,7 @@ export default defineConfig({
           autogenerate: { directory: 'challenges' },
           translations: {
             es: 'Desafíos',
+            'pt-BR': 'Desafios'
           },
         },
       ],
@@ -73,6 +76,10 @@ export default defineConfig({
           label: 'Español',
           lang: 'es',
         },
+        'pt-br': {
+          label: 'Português (Brasil)',
+          lang: 'pt-BR',
+        },
       },
     }),
   ],