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>

internal/web/static/assets/style.css

@@ -346,6 +346,11 @@ button.chip:hover { background: var(--accent-soft); border-color: var(--accent);
 /* Activity: one line per message. */
 table.activity td { white-space: nowrap; }
 table.activity td.detail { white-space: normal; color: var(--muted); }
+table.activity tr.event-details > td { white-space: normal; background: var(--bg); }
+.event-detail table.kv { border-collapse: collapse; margin: 4px 0; }
+.event-detail table.kv th { text-align: left; font-weight: normal; color: var(--muted); padding: 2px 16px 2px 0; vertical-align: top; white-space: nowrap;
+  text-transform: none; letter-spacing: normal; font-size: inherit; background: none; border: 0; }
+.event-detail table.kv td { padding: 2px 0; white-space: normal; word-break: break-word; background: none; border: 0; }
 .type-OFFER, .type-ACK { color: var(--ok); }
 .type-NAK, .type-DECLINE, .type-CONFLICT, .type-NO { color: var(--err); }
 .type-RELEASE { color: var(--muted); }
@@ -355,3 +360,5 @@ input:disabled, select:disabled, textarea:disabled { background: var(--info-soft
 .panel-head { display: flex; align-items: center; justify-content: space-between; gap: 12px; margin-bottom: 8px; }
 .panel-head h2 { margin: 0; }
 pre.wrap { white-space: pre-wrap; word-break: break-all; font-size: 12px; }
+
+.dimmed { opacity: 0.55; }