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/api/types.go

@@ -22,10 +22,10 @@ type Zone struct {
 	Display string `json:"display_name"`
 	View    string `json:"view,omitempty"`
 	Records int    `json:"record_count"`
-	// Disabled is how many of the records are disabled.
-	Disabled int    `json:"disabled_count,omitempty"`
-	ZoneFile string `json:"zone_file,omitempty"` // the file named loads
-	RName    string `json:"rname_email,omitempty"`
+	// DisabledRecords is how many of the records are disabled.
+	DisabledRecords int    `json:"disabled_count,omitempty"`
+	ZoneFile        string `json:"zone_file,omitempty"` // the file named loads
+	RName           string `json:"rname_email,omitempty"`
 	// Registrar names the registrar Jarl can manage the domain at
 	// ("porkbun"), when one is configured for it.
 	Registrar string `json:"registrar,omitempty"`