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/inputs.go

@@ -108,6 +108,8 @@ type ZoneInput struct {
 	// finished, off ("").
 	DNSSECPolicy *string `json:"dnssec_policy,omitempty"`
 	Comment      *string `json:"comment,omitempty"`
+	// Disabled keeps the zone in Jarl but out of named's configuration.
+	Disabled *bool `json:"disabled,omitempty"`
 
 	// Create only: name servers for the apex NS records (default: the
 	// configured default name servers), additional records, and a zone to