TLS certificates: Jarl obtains and renews them over ACME

Jarl is now an ACME client (lego's core, no DNS providers). It answers
DNS-01 challenges in a zone it serves, or through Porkbun's DNS API while
Porkbun serves the domain; "auto" decides from the domain's public name
servers at every renewal, and a CNAME on _acme-challenge is followed.
Certificates are used for jarld's HTTPS (served without a restart; each
port speaks HTTPS and plain HTTP, plain HTTP from loopback and trusted
proxies still served) and/or written for named's DNS over TLS/HTTPS, with
rndc reconfig on renewal. Renewal follows the CA's ARI window or two
thirds of the lifetime, with back-off. Certificates you renew yourself
can be used too. Certificates page and dashboard card, jarl cert,
/api/v1/certificates, Prometheus gauges, docs/certificates.md, and an
e2e section against Pebble.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/api/types.go

@@ -256,6 +256,29 @@ type StatusResponse struct {
 	// BlockingPausedIndefinitely while it is paused until resumed.
 	BlockingPausedUntil        *time.Time `json:"blocking_paused_until,omitempty"`
 	BlockingPausedIndefinitely bool       `json:"blocking_paused_indefinitely,omitempty"`
+	// Certificates sums up the TLS certificates Jarl manages
+	// (administrators only, when there are any).
+	Certificates *CertSummary `json:"certificates,omitempty"`
+}
+
+// CertSummary is what the dashboard reports about certificates.
+type CertSummary struct {
+	Total int `json:"total"`
+	// Problems are the certificates that aren't fine: failing, expiring,
+	// expired (not ones still being obtained for the first time).
+	Problems []CertProblem `json:"problems"`
+	// Next is the certificate that expires first, and when.
+	Next      string     `json:"next,omitempty"`
+	NextAfter *time.Time `json:"next_after,omitempty"`
+	// Serving is the certificate jarld serves HTTPS with ("" for none or tls.cert_file).
+	Serving string `json:"serving,omitempty"`
+}
+
+// CertProblem is a certificate that needs attention.
+type CertProblem struct {
+	Name    string `json:"name"`
+	State   string `json:"state"`
+	Message string `json:"message"`
 }
 
 // BlocklistError is a blocklist whose last update failed. UpdatedAt is