New docs site (#2521)

* initial docs

* more docs work

* Update readme + add license

* update frontend GH action

apps/docs/astro.config.mjs

@@ -0,0 +1,51 @@
+import { defineConfig } from 'astro/config';
+import starlight from '@astrojs/starlight';
+import starlightOpenAPI, { openAPISidebarGroups } from 'starlight-openapi'
+
+// https://astro.build/config
+export default defineConfig({
+  site: 'https://docs.modrinth.com',
+  integrations: [
+    starlight({
+      title: 'Modrinth Documentation',
+      editLink: {
+        baseUrl: 'https://github.com/modrinth/code/edit/main/apps/docs/',
+      },
+      social: {
+          github: 'https://github.com/modrinth/code',
+          discord: 'https://discord.modrinth.com',
+          'x.com': 'https://x.com/modrinth',
+          mastodon: 'https://floss.social/@modrinth',
+          threads: 'https://threads.net/@modrinth',
+      },
+      logo: {
+        light: './src/assets/light-logo.svg',
+        dark: './src/assets/dark-logo.svg',
+        replacesTitle: true,
+      },
+      customCss: [
+        '@modrinth/assets/styles/variables.scss',
+        '@modrinth/assets/styles/inter.scss',
+        './src/styles/modrinth.css',
+      ],
+      plugins: [
+        // Generate the OpenAPI documentation pages.
+        starlightOpenAPI([
+          {
+            base: 'api',
+            label: 'Modrinth API',
+            schema: './public/openapi.yaml',
+          },
+        ])
+      ],
+      sidebar: [
+        {
+            label: 'Contributing to Modrinth',
+            autogenerate: { directory: 'contributing' },
+        },
+        // Add the generated sidebar group to the sidebar.
+        ...openAPISidebarGroups,
+      ],
+    }),
+  ],
+});