feat(docs): new Astro Starlight docs site (Terminal theme)

From-scratch rebuild of the Echo v5 docs on Astro + Starlight with a
custom Terminal theme: homepage hero, Ask Echo island, themed asides,
pager, tables, code blocks and footer; Echo favicon + logo + OG card;
SEO/OG meta; and ~56 content pages (Guide, Middleware, Cookbook) ported
and reviewed against echo/v5 v5.0.4 source.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: vishr

site/.gitignore

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+node_modules/
+dist/
+.astro/
+.DS_Store

site/astro.config.mjs

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+import { defineConfig } from 'astro/config';
+import starlight from '@astrojs/starlight';
+
+// https://astro.build/config
+export default defineConfig({
+  site: 'https://echo.labstack.com',
+  integrations: [
+    starlight({
+      title: 'Echo',
+      logo: {
+        light: './src/assets/logo-light.svg',
+        dark: './src/assets/logo-dark.svg',
+        replacesTitle: true,
+      },
+      customCss: ['./src/styles/terminal.css'],
+      social: [
+        { icon: 'github', label: 'GitHub', href: 'https://github.com/labstack/echo' },
+      ],
+      editLink: {
+        baseUrl: 'https://github.com/labstack/echox/edit/master/website/',
+      },
+      lastUpdated: true,
+      // Echo "E" cube mark; .ico kept as legacy fallback, apple-touch-icon added in head.
+      favicon: '/favicon.svg',
+      // Keep Starlight's built-in Pagefind ⌘K search; add Ask Echo + DocActions via overrides.
+      components: {
+        Footer: './src/components/Footer.astro',
+        PageTitle: './src/components/PageTitle.astro',
+      },
+      head: [
+        // Dark-first: default new visitors to dark unless they've chosen otherwise.
+        {
+          tag: 'script',
+          content: "if(!localStorage.getItem('starlight-theme')){localStorage.setItem('starlight-theme','dark');document.documentElement.dataset.theme='dark';}",
+        },
+        { tag: 'link', attrs: { rel: 'preconnect', href: 'https://fonts.googleapis.com' } },
+        { tag: 'link', attrs: { rel: 'preconnect', href: 'https://fonts.gstatic.com', crossorigin: true } },
+        {
+          tag: 'link',
+          attrs: {
+            rel: 'stylesheet',
+            href: 'https://fonts.googleapis.com/css2?family=DM+Sans:wght@400;500;600;700;800&family=Fragment+Mono&display=swap',
+          },
+        },
+        {
+          tag: 'link',
+          attrs: {
+            rel: 'stylesheet',
+            href: 'https://unpkg.com/@phosphor-icons/web@2.1.1/src/regular/style.css',
+          },
+        },
+        // Default social card. Starlight already emits og:title/description/url
+        // and twitter:card=summary_large_image, but no image — add a site-wide
+        // default so shares aren't imageless. Absolute URLs are required by
+        // social scrapers. Per-page overrides can set their own og:image later.
+        { tag: 'meta', attrs: { property: 'og:image', content: 'https://echo.labstack.com/og.png' } },
+        { tag: 'meta', attrs: { property: 'og:image:width', content: '1200' } },
+        { tag: 'meta', attrs: { property: 'og:image:height', content: '630' } },
+        { tag: 'meta', attrs: { name: 'twitter:image', content: 'https://echo.labstack.com/og.png' } },
+        { tag: 'link', attrs: { rel: 'apple-touch-icon', href: '/apple-touch-icon.png' } },
+      ],
+      // Autogenerated from the content dirs — new pages appear automatically,
+      // ordered by each page's `sidebar.order` frontmatter.
+      sidebar: [
+        { label: 'Guide', items: [{ autogenerate: { directory: 'guide' } }] },
+        { label: 'Middleware', items: [{ autogenerate: { directory: 'middleware' } }] },
+        { label: 'Cookbook', items: [{ autogenerate: { directory: 'cookbook' } }] },
+      ],
+      // tune the built-in code theme toward our terminal palette
+      expressiveCode: { themes: ['github-dark', 'github-light'] },
+    }),
+  ],
+});