Zone settings: no empty changes, keep an outside name server absolute

- A zone update that changes nothing stages nothing: saving a zone's
  settings unchanged says "Nothing changed" instead of staging an empty
  change. Staging operations that change nothing is a 400 "nothing to
  change".
- The settings form showed the SOA MNAME without its final dot, which the
  server reads as relative to the zone, so saving wg.adbraun.lol turned
  ns1.adbraun.lol. into ns1.adbraun.lol.wg.adbraun.lol. Names outside the
  zone keep the dot, and MNAME is only sent when edited.

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

CHANGELOG.md

@@ -19,6 +19,20 @@ All notable changes to Jarl are documented here. The format follows
 - The New token form only offers templates within what the token's user
   may do. A token never does more than its user, so offering more only
   misled.
+- A zone update that changes nothing is no change: saving a zone's
+  settings without changing them says "Nothing changed" instead of
+  staging an empty change. Staging operations that change nothing
+  (`POST /changesets/{id}/ops`, or `?stage=`) is a 400 "nothing to
+  change".
+
+### Fixed
+
+- Saving the settings of a zone whose primary name server is outside it
+  (`ns1.adbraun.lol.` for `wg.adbraun.lol`) changed the name server to
+  `ns1.adbraun.lol.wg.adbraun.lol.`. The form showed the name without its
+  final dot, which the server reads as relative to the zone. Names outside
+  the zone now keep the dot, and the name server is only sent when it was
+  changed.
 
 ## [0.6.0] - 2026-10-13