feat: M15b — OCSP responder, DER CRL, short-lived exemption, revocation GUI

Backend:
- Embedded OCSP responder: GET /api/v1/ocsp/{issuer_id}/{serial} returns
  signed OCSP responses (good/revoked/unknown) using CA key
- DER-encoded X.509 CRL: GET /api/v1/crl/{issuer_id} returns proper DER CRL
  signed by issuing CA with 24h validity window
- Short-lived cert exemption: certs with profile TTL < 1 hour skip CRL/OCSP
  (expiry is sufficient revocation for ephemeral workloads)
- Extended issuer connector interface with GenerateCRL and SignOCSPResponse
- Local CA implements full CRL/OCSP signing; ACME and step-ca return
  appropriate "use native endpoint" errors
- IssuerConnectorAdapter bridges new methods between layers

Frontend:
- Revoke button on certificate detail page with RFC 5280 reason modal
- Revocation banner with reason display and timestamp
- Revocation status indicators in lifecycle section
- "Revoked" filter option in certificates list
- API client: revokeCertificate() function and Certificate type extensions

Tests: ~31 new tests across connector, service, handler, and adapter layers
Docs: milestones renumbered (M13-M14, M16-M18), M15b marked complete

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/api/router/router.go

@@ -90,8 +90,12 @@ func (r *Router) RegisterHandlers(
 	r.Register("POST /api/v1/certificates/{id}/deploy", http.HandlerFunc(certificates.TriggerDeployment))
 	r.Register("POST /api/v1/certificates/{id}/revoke", http.HandlerFunc(certificates.RevokeCertificate))
 
-	// CRL endpoint: /api/v1/crl
+	// CRL endpoints: /api/v1/crl (JSON) and /api/v1/crl/{issuer_id} (DER)
 	r.Register("GET /api/v1/crl", http.HandlerFunc(certificates.GetCRL))
+	r.Register("GET /api/v1/crl/{issuer_id}", http.HandlerFunc(certificates.GetDERCRL))
+
+	// OCSP responder: /api/v1/ocsp/{issuer_id}/{serial}
+	r.Register("GET /api/v1/ocsp/{issuer_id}/{serial}", http.HandlerFunc(certificates.HandleOCSP))
 
 	// Issuers routes: /api/v1/issuers
 	r.Register("GET /api/v1/issuers", http.HandlerFunc(issuers.ListIssuers))