feat(landing): link files. share from nav + hero

Read-only file browse was only reachable by typing the URL. Add
site.filesUrl (files.${BASE_DOMAIN}) plus nav/hero labels in en/es/eu,
and surface it as a nav link and a secondary hero CTA beside "Cómo entrar".

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

landing/src/data/site.ts

@@ -161,6 +161,10 @@ export const site = {
   // Uptime Kuma status page (external link in footer).
   statusUrl: `https://status.${BASE_DOMAIN}`,
 
+  // Public read-only file share (caddy file_server browse of FILES_DATA_DIR).
+  // Linked from the nav + hero. Uploads live at upload.${BASE_DOMAIN} (auth'd).
+  filesUrl: `https://files.${BASE_DOMAIN}`,
+
   // Live server card (ServerCard.astro). `slots` is the SSG fallback cap shown
   // before/without JS; live data comes from our SELF-HOSTED mc-status service
   // (docker/mc-status, mcutil wrapper) reverse-proxied same-origin at the apex