start.sh now generates proxy/caddy.json at launch time with Let's Encrypt
automatic HTTPS (HTTP-01 or TLS-ALPN-01 challenge — no Cloudflare needed).
Reads DOMAIN_SUFFIX and ACME_EMAIL from infra/.env before starting.
Added infra/.env.example to document required vars.
start.sh builds via 'make build' (platform auto-detected) then starts
services detached with 'docker compose up -d'.
Makefile gains build/build-<platform> targets that build images without
starting, mirroring the existing up/<platform> targets.