Tell search engines and link previews what each page is

- /sitemap.xml, from the API's /slugs plus the landing and listings:
  every address in every language, with hreflang and x-default. A 503
  when the API is down, rather than a sitemap missing half the site.
- /robots.txt, naming the sitemap on whatever domain this is served on.
- Slugs renamed in the panel now redirect. The API has always kept the
  old address the moment one changed; middleware/redirects.ts answers
  it with a 301, from a list kept for a minute and through outages.
- og:url, og:image (the record's own picture, the logo otherwise) and
  schema.org JSON-LD: Organization on the landing; WebPage,
  CreativeWork, Person or Service elsewhere. Shared through core/head.
- The proxy-derived origin moves to core/origin.ts, used by the page
  shell, the landing and both server routes.

In development only /api/* reaches Nitro, so the two files 404 under
`npm start`; they were checked against a production build.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

landing/src/server/middleware/redirects.ts

@@ -0,0 +1,59 @@
+/**
+ * Answers an address the panel has retired with a redirect to where the
+ * record lives now, instead of the 404 it would otherwise be.
+ *
+ * The list comes from the API whole — there are never many — and is kept for
+ * a minute, so a page view costs no extra request. If the API does not answer,
+ * the last list that arrived is kept: an outage should not turn every renamed
+ * link back into a 404.
+ */
+import { defineEventHandler, getRequestURL, sendRedirect } from 'h3';
+
+import { pireonApi, type Redirect } from '../../app/core/api';
+import { findRedirect } from '../../app/core/redirects';
+
+const TTL_MS = 60_000;
+
+let cached: Redirect[] = [];
+let loadedAt = 0;
+let pending: Promise<void> | null = null;
+
+async function refresh(): Promise<void> {
+  const { data, error } = await pireonApi.redirects();
+
+  if (!error && data) {
+    cached = data;
+  }
+
+  loadedAt = Date.now();
+}
+
+export default defineEventHandler(async (event) => {
+  if (event.method !== 'GET' && event.method !== 'HEAD') {
+    return;
+  }
+
+  const { pathname } = getRequestURL(event);
+
+  // The app's own endpoints and files are never renamed in the panel.
+  if (
+    /^\/(api|_analog|assets|@|src|node_modules)\//.test(pathname) ||
+    /\.[a-z0-9]+$/i.test(pathname)
+  ) {
+    return;
+  }
+
+  if (Date.now() - loadedAt > TTL_MS) {
+    pending ??= refresh().finally(() => {
+      pending = null;
+    });
+
+    await pending;
+  }
+
+  const redirect = findRedirect(pathname, cached);
+
+  if (redirect) {
+    return sendRedirect(event, redirect.to, redirect.status);
+  }
+});

landing/src/server/routes/robots.txt.get.ts

@@ -0,0 +1,21 @@
+/**
+ * Everything is crawlable, and the sitemap says where everything is. Absolute,
+ * because robots.txt requires it, from whichever domain this is served on.
+ */
+import { defineEventHandler, getRequestHeaders, setResponseHeader } from 'h3';
+
+import { originFromHeaders } from '../../app/core/origin';
+
+export default defineEventHandler((event) => {
+  const origin = originFromHeaders(getRequestHeaders(event)) ?? '';
+
+  setResponseHeader(event, 'Content-Type', 'text/plain; charset=utf-8');
+
+  return [
+    'User-agent: *',
+    'Allow: /',
+    '',
+    `Sitemap: ${origin}/sitemap.xml`,
+    '',
+  ].join('\n');
+});

landing/src/server/routes/sitemap.xml.get.ts

@@ -0,0 +1,34 @@
+/**
+ * `/sitemap.xml`, from the API's `/slugs` — one request for every published
+ * address, instead of paging through each collection.
+ *
+ * Cached like any page: a record published a minute ago can wait a minute to
+ * be listed. If the API is down the answer is a 503 rather than a sitemap
+ * with half the site missing from it, which a crawler would believe.
+ */
+import {
+  defineEventHandler,
+  getRequestHeaders,
+  setResponseHeader,
+  setResponseStatus,
+} from 'h3';
+
+import { pireonApi } from '../../app/core/api';
+import { originFromHeaders } from '../../app/core/origin';
+import { buildSitemap } from '../../app/core/sitemap';
+
+export default defineEventHandler(async (event) => {
+  const origin = originFromHeaders(getRequestHeaders(event)) ?? '';
+  const { data } = await pireonApi.slugs();
+
+  if (!data) {
+    setResponseStatus(event, 503);
+    setResponseHeader(event, 'Cache-Control', 'no-store');
+
+    return 'Sitemap temporarily unavailable';
+  }
+
+  setResponseHeader(event, 'Content-Type', 'application/xml; charset=utf-8');
+
+  return buildSitemap(origin, data);
+});