feat(website): add the fl.narl.io site

Astro site for the suite: a home page with the plugin cards, install
steps, principles, the metalwork names and the ideas on the bench, one
page per plugin, and the Impressum and privacy policy. Plugin names,
versions, download links and editor previews come from the catalog, the
wrapper manifests and docs/*/assets at build time.

Served by unprivileged nginx in Docker behind Traefik on fl.narl.io,
the same setup as proton.narl.io: no access logs, CSP 'self', no
JavaScript, legal pages filled from the environment at start.

website/.env.example

@@ -0,0 +1,21 @@
+# Copy to .env and fill in. The container refuses to start while a required value is missing,
+# so the site never goes live without an Impressum.
+
+# Public URL of the site, used for canonical links, the sitemap and robots.txt (build time).
+SITE_URL=https://fl.narl.io
+
+# Impressum (§ 5 DDG) and controller in the privacy policy. Required.
+# The address must be one where legal documents can be served: no P.O. box.
+IMPRESSUM_NAME=Max Mustermann
+IMPRESSUM_STREET=Musterstraße 1
+IMPRESSUM_CITY=12345 Musterstadt
+IMPRESSUM_EMAIL=kontakt@example.org
+
+# Optional. Defaults to "Deutschland".
+IMPRESSUM_COUNTRY=Deutschland
+# Optional. Leave empty to hide the phone line.
+IMPRESSUM_PHONE=
+# Optional. Name and address of the hosting provider, if one processes visitor data for you
+# (Art. 28 GDPR), e.g. "Hetzner Online GmbH, Industriestr. 25, 91710 Gunzenhausen".
+# Leave empty to hide that paragraph.
+HOSTER=