Add DNSSEC signing, key backups and Porkbun support

Zones get a DNSSEC setting: named signs them with BIND's default (or a
custom) dnssec-policy and inline signing, with keys in a per-view key
directory. Jarl shows the keys, the DS record and when it is safe to
publish it, checks the parent's DS records (check-ds, which also tells
named), and refuses steps that would break a signed domain: switching
straight to unsigned, finishing a turn-off too early, deleting or moving
a signed zone, TTLs above max-zone-ttl. Turning off goes through the
insecure policy; wipe starts over once the parent has no DS.

Backups store the DNSSEC keys and restore puts them back for named; the
backup unit gets CAP_DAC_READ_SEARCH to read them. Jarl raises a zone's
serial above named's whenever it writes an older one (after a restore).
The serials check compares the signed serial.

With a Porkbun API key in jarl.yaml, the registrar's name servers, glue
records and DS records can be shown and changed, each change checked
first (dry run, force to override).

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

internal/server/server.go

@@ -20,6 +20,7 @@ import (
 	"jarl/internal/auth"
 	"jarl/internal/engine"
 	"jarl/internal/nscheck"
+	"jarl/internal/porkbun"
 	"jarl/internal/stats"
 	"jarl/internal/store"
 )
@@ -47,6 +48,10 @@ type Config struct {
 	// reports on (backup.dir and backup.warn_after).
 	BackupDir       string
 	BackupWarnAfter time.Duration
+	// Porkbun manages domains' delegation at the registrar Porkbun (nil
+	// without an API key); PorkbunAllows says which domains it may touch.
+	Porkbun       *porkbun.Client
+	PorkbunAllows func(domain string) bool
 }
 
 // Server is the HTTP server.