Fix "update PTR": add a missing PTR, also in linked views

Ticking update PTR alone did nothing: the web UI didn't send it, and the engine only acted when the name or address changed. Alone it now adds a missing PTR record (or enables it); for linked zones every linked view's reverse zone counts.

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

internal/engine/inputs.go

@@ -174,7 +174,9 @@ type RecordInput struct {
 	// Disabled keeps the record in Jarl but out of the zone.
 	Disabled *bool `json:"disabled,omitempty"`
 	// PTR also creates (or deletes, disables or enables) the matching PTR
-	// record in the reverse zone, for A and AAAA records.
+	// record in the reverse zone, for A and AAAA records. On an update that
+	// changes nothing else it adds the PTR record if it is missing. In a
+	// linked zone, every linked view's reverse zone counts.
 	PTR bool `json:"ptr,omitempty"`
 	// MissingOK makes a delete-by-match succeed when nothing matches.
 	MissingOK bool `json:"missing_ok,omitempty"`