Support Let's Encrypt short-lived certificate profiles

[nullcert]

Operator problem: short-lived certificates make automation quality visible and reduce reliance on revocation, but lego requires the ACME profile field and the MVP deliberately treats that field as unsupported. The production website therefore cannot honestly enable the shortlived profile without expanding AcmeMux compatibility and tests. Proposed outcome: qualify the shortlived profile for supported CAs, add typed configuration, preserve profile semantics in operation review, add compatibility tests, and document renewal timing and failure margins. Vote with one positive reaction if this should be the next community-priority feature. Organizations interested in selecting this accepted work for fast-track priority can use https://acmemux.com/sponsor/.