feat: generate /fr/sitemap.xml via custom Nitro route

@nuxtjs/sitemap is incompatible with app.baseURL: '/fr/' here — it broke
nginx routing (403) on this deployment where /fr/ is served via an alias
to a separate static build. A hand-rolled Nitro route sidesteps the
module entirely and gets prerendered to a plain sitemap.xml file at the
root of the generated output, matching what the nginx alias expects.

server/routes/sitemap.xml.ts

@@ -0,0 +1,23 @@
+import { serverQueryContent } from '#content/server'
+
+// generates /fr/sitemap.xml without @nuxtjs/sitemap (incompatible with baseURL /fr/)
+export default defineEventHandler(async (event) => {
+  const docs = await serverQueryContent(event).find()
+
+  const urls = docs
+    .filter((doc: any) =>
+      doc._path &&
+      !doc._path.startsWith('/_') &&
+      !doc._path.endsWith('/_dir')
+    )
+    .map((doc: any) => `  <url><loc>https://docu.djeex.fr/fr${doc._path}</loc></url>`)
+    .join('\n')
+
+  const sitemap = `<?xml version="1.0" encoding="UTF-8"?>
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+${urls}
+</urlset>`
+
+  setHeader(event, 'Content-Type', 'application/xml')
+  return sitemap
+})