Switch from a custom caddy-dns/gandi image built on-host to the official
caddy:2 image with per-host ACME HTTP-01 certificates. Removes the
Dockerfile, env.j2 (Gandi token), on-host image build/ship/load tasks,
the caddy-image Makefile target, and the wildcard DNS-01 Caddyfile.
Each route now gets its own server block and automatic certificate.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>