fix(seo): noindex staging builds by default

- add PUBLIC_ALLOW_INDEXING as an explicit production indexing opt-in
- emit robots meta noindex,nofollow unless indexing is enabled
- generate robots.txt from the same indexing flag
- document staging SEO behavior for migration preview hosts

www/.env.example

@@ -1 +1,2 @@
 PUBLIC_AIA_API_BASE=https://api.azinstitute4autism.com
+PUBLIC_ALLOW_INDEXING=false

www/README.md

@@ -38,19 +38,23 @@ cd www
 npm install
 ```
 
-Copy the example environment file when testing the like/view counter:
+Copy the example environment file when testing the like/view counter or staging
+SEO behavior:
 
 ```sh
 cp .env.example .env
 ```
 
-The default value is:
+The default values are:
 
 ```txt
 PUBLIC_AIA_API_BASE=https://api.azinstitute4autism.com
+PUBLIC_ALLOW_INDEXING=false
 ```
 
-The site still renders when that API is unavailable.
+The site still renders when the AIA API is unavailable. Migration and staging
+builds emit `noindex,nofollow` by default; set `PUBLIC_ALLOW_INDEXING=true`
+only for production builds on the canonical domain.
 
 ## View And Build
 

www/public/robots.txt

@@ -1,3 +0,0 @@
-User-agent: *
-Allow: /
-Sitemap: https://www.azinstitute4autism.com/sitemap.xml

www/src/components/Seo.astro

@@ -6,12 +6,23 @@ interface Props {
   image?: string;
   lang?: string;
   type?: 'website' | 'article';
+  robots?: string;
 }
-const { title, description = '', canonical, image, lang = 'en', type = 'website' } = Astro.props;
+const {
+  title,
+  description = '',
+  canonical,
+  image,
+  lang = 'en',
+  type = 'website',
+  robots
+} = Astro.props;
+const defaultRobots = import.meta.env.PUBLIC_ALLOW_INDEXING === 'true' ? 'index,follow' : 'noindex,nofollow';
 const absoluteImage = image ? new URL(image, Astro.site ?? Astro.url).href : undefined;
 ---
 <title>{title}</title>
 <meta name="description" content={description} />
+<meta name="robots" content={robots ?? defaultRobots} />
 {canonical && <link rel="canonical" href={canonical} />}
 <meta property="og:type" content={type} />
 <meta property="og:title" content={title} />

www/src/pages/robots.txt.ts

@@ -0,0 +1,23 @@
+const allowIndexing = import.meta.env.PUBLIC_ALLOW_INDEXING === 'true';
+
+const body = allowIndexing
+  ? [
+      'User-agent: *',
+      'Allow: /',
+      'Sitemap: https://www.azinstitute4autism.com/sitemap.xml',
+      ''
+    ].join('\n')
+  : [
+      'User-agent: *',
+      'Allow: /',
+      '# Staging and migration builds emit meta robots noindex,nofollow.',
+      ''
+    ].join('\n');
+
+export function GET() {
+  return new Response(body, {
+    headers: {
+      'Content-Type': 'text/plain; charset=utf-8'
+    }
+  });
+}