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>

docs/cli.md

@@ -211,6 +211,18 @@ router, answers for the rest of the /24. IPv4 networks smaller than a /24
 are deleted. Try it with `--dry-run` first. `--option "NAME VALUE"` on
 `zone create` sets any zone option in the same step.
 
+Linked zones ([views.md](views.md#linked-zones)) keep their shared
+records in step across views:
+
+```sh
+jarl zone link adbraun.lol --view internal --with external
+jarl zone create adbraun.lol --view vps --link-with external
+jarl zone unlink adbraun.lol --view vps
+jarl record add adbraun.lol nas A 10.0.10.20 --view internal --local   # this view only
+jarl record set adbraun.lol www A 10.0.10.5 --view internal --local    # override the shared www A here
+jarl record update 1234 --local | --shared
+```
+
 When a zone exists in several views, add `--view NAME` to commands that
 name it.