fix: end-to-end certificate lifecycle bugs + integration test environment

Fixes 12 production bugs preventing the full issuance→deployment flow
from working with ACME (Pebble/Let's Encrypt) and step-ca issuers:

ACME connector (acme.go):
- Save orderURI before WaitOrder overwrites it (Go crypto/acme bug)
- Add CreateOrderCert fallback via WaitOrder+FetchCert
- Remove defer-reset in ValidateConfig that caused nil pointer panic
- Add Insecure TLS option for self-signed ACME servers (Pebble)

step-ca connector (stepca.go, jwe.go):
- Real JWE provisioner key loading + decryption (was using ephemeral keys)
- Fix JWT audience (/1.0/sign), sha claim (key fingerprint), kid header
- Custom root CA trust via RootCertPath config
- Remove hardcoded 90-day validity default (let step-ca decide)

NGINX target connector (nginx.go):
- Use sh -c for validate/reload commands (shell interpretation)
- Use filepath.Dir instead of fragile string slicing
- Add private key file writing (agent-mode keys were never deployed)
- Make chain_path write conditional

Server/service layer:
- TriggerRenewalWithActor now creates actual Job records (was no-op)
- createDeploymentJobs falls back to DB query when cert.TargetIDs empty
- ProcessPendingJobs skips agent-routed deployment jobs
- Agent cert pickup path parsing: len(parts)<4 → len(parts)<3
- Health/ready/auth-info endpoints bypass auth middleware
- Write timeout 15s→120s for ACME issuance
- Cert fingerprint computed on CSR submission

Integration test environment (deploy/test/):
- 10-phase test script covering Local CA, ACME, step-ca, revocation,
  discovery, renewal, and API spot checks
- Docker Compose with 7 containers (server, agent, postgres, nginx,
  pebble, challtestsrv, step-ca) on isolated network
- TLS verification checks SAN (not just Subject CN) for modern CA compat

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

internal/api/handler/agents.go

@@ -252,6 +252,7 @@ func (h AgentHandler) AgentCSRSubmit(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if err != nil {
+		slog.Error("CSR submission failed", "agent_id", agentID, "certificate_id", req.CertificateID, "error", err.Error())
 		ErrorWithRequestID(w, http.StatusInternalServerError, "Failed to submit CSR", requestID)
 		return
 	}
@@ -274,9 +275,10 @@ func (h AgentHandler) AgentCertificatePickup(w http.ResponseWriter, r *http.Requ
 	requestID := middleware.GetRequestID(r.Context())
 
 	// Extract agent ID and certificate ID from path /api/v1/agents/{id}/certificates/{cert_id}
+	// After TrimPrefix, path is "{id}/certificates/{cert_id}" → split gives [id, "certificates", cert_id]
 	path := strings.TrimPrefix(r.URL.Path, "/api/v1/agents/")
 	parts := strings.Split(path, "/")
-	if len(parts) < 4 || parts[0] == "" || parts[2] == "" {
+	if len(parts) < 3 || parts[0] == "" || parts[2] == "" {
 		ErrorWithRequestID(w, http.StatusBadRequest, "Agent ID and Certificate ID are required", requestID)
 		return
 	}