Disable records instead of deleting them

A disabled record stays in Jarl with its ID, TTL and comment but is
left out of the zone; the zone file lists it as a comment. Web UI
toggle, jarl record disable|enable, record.disable|enable operations
and API endpoints. Database schema 5.

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

internal/model/model.go

@@ -154,6 +154,9 @@ type Record struct {
 	TTL     *uint32 `json:"ttl,omitempty"`
 	Data    string  `json:"data"` // canonical presentation format
 	Comment string  `json:"comment"`
+	// Disabled records stay in Jarl but are left out of the zone (the
+	// zone file lists them as comments).
+	Disabled bool `json:"disabled,omitempty"`
 	Meta
 }
 
@@ -446,6 +449,18 @@ func (s *State) ZoneRecords(zoneID int64) []*Record {
 	return out
 }
 
+// ServedRecords returns the records of a zone that are in the zone file
+// (not disabled), in display order.
+func (s *State) ServedRecords(zoneID int64) []*Record {
+	var out []*Record
+	for _, r := range s.ZoneRecords(zoneID) {
+		if !r.Disabled {
+			out = append(out, r)
+		}
+	}
+	return out
+}
+
 // RecordsByZone groups all records by zone ID (unsorted).
 func (s *State) RecordsByZone() map[int64][]*Record {
 	out := map[int64][]*Record{}
@@ -455,6 +470,17 @@ func (s *State) RecordsByZone() map[int64][]*Record {
 	return out
 }
 
+// ServedRecordsByZone is RecordsByZone without disabled records.
+func (s *State) ServedRecordsByZone() map[int64][]*Record {
+	out := map[int64][]*Record{}
+	for _, r := range s.Records {
+		if !r.Disabled {
+			out[r.ZoneID] = append(out[r.ZoneID], r)
+		}
+	}
+	return out
+}
+
 // ScopedOptions returns the options of a scope, in position order.
 func (s *State) ScopedOptions(scope string, scopeID int64) []*Option {
 	var out []*Option