Linked zones: shared records kept in step across views

Zones of the same name in different views can be linked. Shared records
are kept in step: a change in one view reaches the others in the same
changeset, as explicit operations, so the diff, permission checks,
history and undo cover every view. Records local to a view override the
shared records of that name and type there; removing the override brings
the shared ones back, and sharing a view's version makes it every view's.
Each zone keeps its own options, serial and file.

Linking existing zones changes no answer: what is the same everywhere
becomes shared, the rest stays local. Unlinking keeps every record, all
local. ACME challenges are written once per link, and --view all changes
a link once. jarl zone link/unlink, zone create --link-with, record
--local/--shared, LINK column, web UI controls, POST /zones/{zone}/link
and /unlink, validation checks linked_*, store migration 11, docs and
e2e.

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

internal/server/present.go

@@ -22,6 +22,9 @@ func (s *Server) presentZone(st *model.State, z *model.Zone, counts map[int64]re
 		out.RName = dnsname.EmailFromMailbox(z.SOA.RName)
 	}
 	out.Registrar = s.registrarFor(z)
+	for _, o := range st.LinkedWith(z) {
+		out.LinkedWith = append(out.LinkedWith, st.ViewName(o))
+	}
 	return out
 }
 
@@ -30,6 +33,12 @@ func presentRecord(st *model.State, r *model.Record) api.Record {
 	out := api.Record{Record: *r}
 	if z != nil {
 		out.Zone, out.View, out.RelativeName, out.EffectiveTTL = z.Name, st.ViewName(z), dnsname.Relative(r.Name, z.Name), r.EffectiveTTL(z)
+		if z.LinkGroup != 0 {
+			out.Linked = "local"
+			if r.SharedID != 0 {
+				out.Linked = "shared"
+			}
+		}
 		if rr.IsTextType(r.Type) {
 			if p, err := rr.Parse(z.Name, r.Name, r.Type, r.Data); err == nil {
 				if t, ok := rr.TextValue(p.RR); ok {