jumoo-simple-site: build the simplified jumoo.co.uk

Built the simplified jumoo.co.uk from scratch — static Eleventy site (markdown + JSON data, hand-written CSS, no framework), replacing the old site, focused on uSync and Translation Manager
Added a daily scheduled workflow that fetches live NuGet versions for uSync/uSync.Complete/Translation Manager instead of hand-maintained numbers — caught and fixed a bug where a generatedAt timestamp made it commit a no-op every run
Checked every docs.jumoo.co.uk link against the docs site's actual sitemap rather than trusting the old copy — found and fixed five that had been broken since the port