feat: establish public SEO foundation

apps/web/src/pages/sitemap.xml.ts

@@ -0,0 +1,19 @@
+import type { APIRoute } from "astro";
+import { api, type Activity } from "../lib/api";
+
+const escapeXml = (value: string) => value.replace(/[<>&'\"]/g, character => ({ "<": "&lt;", ">": "&gt;", "&": "&amp;", "'": "&apos;", '"': "&quot;" })[character] ?? character);
+
+export const GET: APIRoute = async ({ site }) => {
+  const origin = site?.origin ?? import.meta.env.PUBLIC_SITE_URL ?? "https://rf4spotter.ru";
+  const paths = new Set(["/", "/records", "/report", "/rules", "/privacy"]);
+  try {
+    const activity = await api<Activity[]>("/api/v1/activity?hours=72&limit=100");
+    activity.forEach(item => paths.add(`/spots/${item.spot_id}`));
+  } catch {
+    // A temporary API outage must not make the static part of the sitemap unavailable.
+  }
+  const urls = [...paths].map(path => `<url><loc>${escapeXml(new URL(path, origin).toString())}</loc></url>`).join("");
+  return new Response(`<?xml version="1.0" encoding="UTF-8"?><urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">${urls}</urlset>`, {
+    headers: { "Content-Type": "application/xml; charset=utf-8", "Cache-Control": "public, max-age=1800" },
+  });
+};