Allow and deny lists per subnet; every option of a DHCP message in words

- A subnet is a deny-list subnet (the default: everyone not denied) or
  an allow-list subnet (only clients allowed or with a reservation);
  the deny list counts in both. Entries are MAC addresses, prefixes
  (aa:bb:cc:*) or client IDs. A refused client gets no answer (DENIED
  in the activity log, with an Allow button) or a NAK on renewal.
  steward access, the subnet's Access tab. Schema migration 7.
- The activity log keeps each message's header fields and options,
  decoded into words (dhcp4.Describe): the parameter request list by
  name, client IDs, lease times. ▸ on an Activity row, steward
  activity show N / --details, GET /events/{id}.

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

docs/api.md

@@ -99,6 +99,10 @@ Creating answers 201, other changes 200.
  "options": [{"option": "routers", "value": "10.0.10.1"}], "disabled": false, "comment": ""}
 ```
 
+`access` is `deny-list` (the default, left out) or `allow-list`; `allow`
+and `deny` replace the lists, each `[{"match": "aa:bb:cc:*", "comment":
+"Sonos"}]` with a MAC address, a prefix or `"id HEX"`
+([subnets.md](subnets.md#access-allow-and-deny-lists)).
 `pools` and `options` replace the lists; the pools keep their order. A
 pool's `:ORDER` is its own address order. `pool_order` is `listed` or
 `random`; `address_order` is `sequential`, `reverse`, `random` or
@@ -122,7 +126,8 @@ out. `lease_time` 0 means the settings'.
 | `GET /leases/{ip}` | one |
 | `DELETE /leases/{ip}` | forget it (audited) |
 | `POST /leases/{ip}/reserve` | make it a reservation; optional `{"hostname", "comment", "by"}`, `by` being `mac`, `client_id` or `both` (the default) |
-| `GET /events[?mac=&subnet=&interface=&limit=]` | the latest DHCP messages, newest first (the last 1000 are kept in memory). `subnet` (ID, name or prefix) keeps messages for its addresses, and those without an address on its interface |
+| `GET /events[?mac=&subnet=&interface=&limit=&details=1]` | the latest DHCP messages, newest first (the last 1000 are kept in memory), each with an `id`, `direction` (`in` from the client, `out` from Steward) and `client_id`. `subnet` (ID, name or prefix) keeps messages for its addresses, and those without an address on its interface. `details=1` adds `fields` and `options` |
+| `GET /events/{id}` | one message with `fields` (header fields that are set) and `options`, each `{"code", "name", "value"}` in words |
 
 ### History and import