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/web/static/assets/pages/zone.js

@@ -625,7 +625,7 @@ async function recordsTab(el, zone, query) {
     const eTTL = input({ type: "number", value: r.ttl ?? "", placeholder: "default", style: { width: "90px" } });
     const eData = input({ value: r.type === "TXT" && r.text !== undefined ? r.text : r.data, class: "mono", style: { width: "100%" } });
     const eComment = input({ value: r.comment || "", style: { width: "100%" } });
-    const ePTR = checkbox("update PTR", false);
+    const ePTR = checkbox("update PTR", false, { title: "Keep the PTR record in the reverse zone in step: moved with a new name or address, or added if it is missing" });
     const eErr = h("div");
     const save = async () => {
       const body = {};
@@ -638,7 +638,9 @@ async function recordsTab(el, zone, query) {
       else if (eTTL.value !== "" && Number(eTTL.value) !== r.ttl) body.ttl = Number(eTTL.value);
       if (eComment.value !== (r.comment || "")) body.comment = eComment.value;
       if (ePTR.input.checked) body.ptr = true;
-      if (Object.keys(body).length === 0 || (Object.keys(body).length === 1 && body.ptr)) { editing = null; draw(); return; }
+      // "update PTR" alone adds a missing PTR record (the reverse zone may
+      // be newer than the record).
+      if (Object.keys(body).length === 0) { editing = null; draw(); return; }
       try {
         const res = await change("PATCH", "/records/" + r.id, body);
         toast(describeResult(res));