New optional dateFormat field in config.json: tokens YYYY, MM, DD are replaced by year/month/day, everything else renders verbatim, so "DD.MM.YYYY" (European), "DD/MM/YYYY" or "YYYY/MM/DD" are one-liners.
- Config.DateLayout() maps the tokens to a Go reference-time layout (YYYY->2006, MM->01, DD->02); empty/absent -> the ISO default
- applies to the human-visible date text on post pages, the home post list and cards, the archive and tag pages
- protocol dates stay ISO 8601 by design:
- default keeps existing sites byte-identical (showcase rebuild = 0 changed files); tests: layout mapping, config default/override, end-to-end DD.MM.YYYY build across all five render sites + sitemap