fix: harden Haraka TLS (renegotiation DoS + untrusted cert chain)

[taobojlen]

Summary

Fixes two security scanner findings on app.shroud.email:25 (the Haraka SMTP TLS path):

1. Client-initiated TLS renegotiation (DoS)

haraka/haraka_config/config/tls.ini — set secureOptions=1073741824 (=crypto.constants.SSL_OP_NO_RENEGOTIATION). Haraka's tls_socket.js passes secureOptions from tls.ini [main] straight to tls.createSecureContext / TLSSocket, so this refuses renegotiation on every STARTTLS upgrade (ports 25 and 465), closing the CPU-exhaustion vector where an attacker forces repeated handshakes.

2. Untrusted certificate on port 25

cron/bundle_certs.sh + cron/Dockerfile — the daily bundle appended a hardcoded, now-expired Let's Encrypt intermediate (lets-encrypt-r4.pem, expired 2025-09-15) to Caddy's fullchain, producing leaf + correct_intermediate + expired_R4 → broken chain → untrusted. Caddy's {domain}.crt is already the full chain (leaf + intermediates); copy it verbatim and delete the stale intermediate. Also:

• Run the bundle at container startup (not only daily) so a fresh pem_certs volume is populated before Haraka's first STARTTLS.
• No-op gracefully (exit 0) when Caddy hasn't issued yet, so a cold boot where ACME is still running doesn't crash crond.

Test plan

• docker compose build cron && docker compose up -d --build cron haraka — verify Haraka starts and presents a valid chain on port 25.
• openssl s_client -starttls smtp -connect app.shroud.email:25 -showcerts </dev/null | openssl x509 -noout -issuer -subject — issuer is a current Let's Encrypt intermediate (R10/R11), not R4.
• openssl s_client -starttls smtp -connect app.shroud.email:25 -CAfile /etc/ssl/cert.pem -verify_return_error </dev/null — Verify return code: 0 (ok).
• Renegotiation refused: a forced renegotiation (printf 'R\n' | openssl s_client -starttls smtp -connect app.shroud.email:25) returns an alert/reset while the initial handshake still succeeds.
• Re-run the scanner against app.shroud.email:25; both findings clear.

Notes

• No hardcoded intermediate to maintain going forward — Caddy owns the chain, including future rotations (R10→R11→…).
• secureOptions does not inherit into Haraka's [outbound] section, but renegotiation isn't a DoS risk on outbound (we're the client), so this is intentional.