Sets from Jarl: sets holding the addresses of names in Jarl

A set can take its addresses from Jarl: every A and AAAA record of its
names (NAME@VIEW), CNAMEs followed within Jarl's zones in the same view.
housecarld reads them every jarl.refresh and after each change, keeps
only the addresses within the zones and networks the set allows, and
keeps what it last read (saved in the database and the boot ruleset)
while Jarl can't be reached. A change of the addresses applies the
ruleset again without a history entry and is audited (set.jarl).

hc set add --jarl --within, hc set jarl; the kind "from Jarl" and
Addresses… on the Sets page; GET /sets/{name}/jarl and /jarl/refresh;
validation codes set_jarl_*, status warnings jarl_*; docs/jarl.md.
e2e phase with scripts/fakejarl.

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

docs/design.md

@@ -94,7 +94,8 @@ table inet housecarl { ... }
 Two things survive the replacement: the **entries of dynamic sets**
 (read before, written back with their remaining timeouts, in the same
 script), and the **counters** (housecarld adds the old totals to the
-new, so hits don't reset with every change).
+new, so hits don't reset with every change). Sets from Jarl are written
+with the addresses last read from Jarl.
 
 Every rule carries a comment `hc:<mark>`, such as `hc:r12` for rule 12,
 `hc:f3` for port forward 3, `hc:b-established` for a built-in. Counters
@@ -199,8 +200,15 @@ Housecarl's replaces it ([import.md](import.md)).
   may only change that set (`sets:write:guests`). Addresses, not MAC
   addresses: matching by MAC only works on the guests' own network
   segment.
-* **Names instead of addresses**: Steward knows every reservation's
-  address and Jarl every name, so rules could name a device or a subnet.
+* **Names instead of addresses**: a set can take its addresses from Jarl
+  ([jarl.md](jarl.md#sets-from-jarl)). housecarld reads the names' A and
+  AAAA records through Jarl's API (CNAMEs followed, one view per name)
+  and keeps the addresses that lie within the zones and networks the set
+  allows; Jarl never calls Housecarl. What was last read is kept (in the
+  database too) while Jarl can't be reached. A change of the addresses
+  applies the ruleset again without a history entry, as dynamic sets'
+  entries aren't in it either. Names Steward makes from leases must not
+  be used: a client chooses its own hostname.
 * **The web UI's certificate** comes through Jarl, as Steward's does
   ([certificates.md](certificates.md)).