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>

docs/cli.md

@@ -307,7 +307,9 @@ adds the quotes and splits long values into 255-byte strings. In reverse zones t
 host name (a bare `nas` is refused, since it would mean
 `nas.0.10.10.in-addr.arpa.`). `--ptr`
 keeps the PTR record in the reverse zone in step (when that zone is managed
-by Jarl). Every record type BIND supports can be used. Jarl knows the
+by Jarl); `jarl record update ID --ptr` with nothing else adds the PTR record
+if it is missing, e.g. after creating the reverse zone. In linked zones, the
+reverse zones of every linked view count. Every record type BIND supports can be used. Jarl knows the
 syntax of the common ones and checks them strictly, and the rest are
 validated by parsing.