simple-site: Translation Manager pages and connector feed

simple-site: new Translation Manager workflow and data-handling pages
simple-site: overhauled the Translation Manager features page and turned the overview into a summary
simple-site: Translation Manager connector feed served from the site, with the CSV and Umbraco.AI connectors added and each AI translator listed as its own connector
simple-site: feed keys kept out of connectors.json
simple-site: /resend now redirects to checkout instead of being proxied
simple-site: headings switched to Barlow Regular to match the live site