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/engine/ops.go

@@ -373,7 +373,7 @@ func parseRecord(z *model.Zone, name, typ, data string) (string, *rr.Parsed, err
 
 func rrsetTTL(st *model.State, zoneID int64, name, typ string, exceptID int64) (*uint32, bool) {
 	for _, r := range st.Records {
-		if r.ZoneID == zoneID && r.Name == name && r.Type == typ && r.ID != exceptID {
+		if r.ZoneID == zoneID && r.Name == name && r.Type == typ && r.ID != exceptID && !r.Disabled {
 			if r.TTL == nil {
 				return nil, true
 			}
@@ -422,6 +422,9 @@ func applyRecordCreate(st *model.State, op model.Op, c *applyCtx) error {
 	if in.Comment != nil {
 		r.Comment = *in.Comment
 	}
+	if in.Disabled != nil {
+		r.Disabled = *in.Disabled
+	}
 	for _, w := range p.Warnings {
 		c.warn("%s %s: %s", dnsname.Display(owner), p.Type, w)
 	}
@@ -498,6 +501,9 @@ func applyRecordUpdate(st *model.State, op model.Op, c *applyCtx) error {
 	if in.Comment != nil {
 		r.Comment = *in.Comment
 	}
+	if in.Disabled != nil {
+		r.Disabled = *in.Disabled
+	}
 	r.Touch(c.user(), c.now)
 	return nil
 }
@@ -617,20 +623,32 @@ func applyRRSetReplace(st *model.State, op model.Op, c *applyCtx) error {
 	} else if t, ok := rrsetTTL(st, z.ID, owner, typ, 0); ok {
 		ttl, ttlKnown = t, true
 	}
+	// The RRset becomes exactly the given data. A disabled record with
+	// one of the values is enabled again; other disabled records are left
+	// alone.
 	keep := map[string]bool{}
-	for id, r := range st.Records {
+	// (In ID order, so which of two identical records is kept doesn't
+	// depend on map order.)
+	for _, id := range sortedKeys(st.Records) {
+		r := st.Records[id]
 		if r.ZoneID != z.ID || r.Name != owner || r.Type != typ {
 			continue
 		}
 		k := strings.ToLower(r.Data)
 		if seen[k] && !keep[k] {
 			keep[k] = true
-			if ttlKnown && !sameTTL(r.TTL, ttl) {
-				r.TTL = copyTTL(ttl)
+			if (ttlKnown && !sameTTL(r.TTL, ttl)) || r.Disabled {
+				if ttlKnown {
+					r.TTL = copyTTL(ttl)
+				}
+				r.Disabled = false
 				r.Touch(c.user(), c.now)
 			}
 			continue
 		}
+		if r.Disabled {
+			continue
+		}
 		delete(st.Records, id)
 	}
 	ids := in.NewIDs