feat(web): hint about {{domain_name}} placeholder in template editor

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/components/RecordEditor.tsx

@@ -1,7 +1,8 @@
-import { Plus, Trash2 } from "lucide-react"
+import { Info, Plus, Trash2 } from "lucide-react"
 import { Button } from "@/components/ui/button"
 import { Input } from "@/components/ui/input"
 import { Textarea } from "@/components/ui/textarea"
+import { FieldDescription } from "@/components/ui/field"
 import {
   Select,
   SelectContent,
@@ -42,6 +43,15 @@ export function RecordEditor({
 
   return (
     <div className="flex flex-col gap-2">
+      <FieldDescription className="flex items-start gap-2 rounded-lg border border-border/60 bg-background/40 px-3 py-2.5">
+        <Info className="mt-0.5 size-3.5 shrink-0 text-muted-foreground" strokeWidth={1.75} />
+        <span>
+          Используйте <code className="font-dns text-foreground">{"{{domain_name}}"}</code> в имени
+          или значении записи — при проверке домена подставится имя его зоны (без завершающей
+          точки).
+        </span>
+      </FieldDescription>
+
       {value.map((record, index) => (
         <div
           key={index}