Disable zones instead of deleting them

A disabled zone stays in Jarl with its records, options and history,
still editable, but named doesn't load it; enabling it serves it as it is
then. Signed zones, and zones another view shares, can't be disabled.
jarl zone disable|enable, the zone page's Disable/Enable button.
Database schema 7.

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

internal/engine/engine.go

@@ -477,12 +477,12 @@ func (e *Engine) makePlan(ctx context.Context, base, work *model.State, user str
 		changedPaths[f.Path] = true
 	}
 	for _, z := range work.SortedZones() {
-		if z.Type != model.ZonePrimary {
-			continue
+		if z.Type != model.ZonePrimary || z.Disabled {
+			continue // disabled zones aren't in named: nothing to reload
 		}
 		path := pl.out.ZoneFiles[z.ID]
 		old := base.Zones[z.ID]
-		existedInNamed := old != nil && old.Type == model.ZonePrimary && baseOut.ZoneFiles[old.ID] == path
+		existedInNamed := old != nil && old.Type == model.ZonePrimary && !old.Disabled && baseOut.ZoneFiles[old.ID] == path
 		if !existedInNamed {
 			pl.newZones = true
 			pl.verify[z.ID] = z.SOA.Serial
@@ -1054,7 +1054,7 @@ func (e *Engine) Resync(ctx context.Context, p *auth.Principal, opts ApplyOption
 	pl.configChanged = true
 	pl.reloadZones = nil
 	for _, z := range work.SortedZones() {
-		if z.Type == model.ZonePrimary {
+		if z.Type == model.ZonePrimary && !z.Disabled {
 			pl.reloadZones = append(pl.reloadZones, z)
 			pl.verify[z.ID] = z.SOA.Serial
 		}