Hidden interfaces, last-seen pings, activity by subnet

- interfaces.exclude in steward.yaml (names or shell patterns) leaves
  interfaces out of GET /interfaces, the web UI's picker and
  'steward interface list'. Subnets on them are still served.
- With the ping check on, active leases are pinged every minute; a
  client that answers gets a last-seen time (leases.last_seen,
  migration 4). Not answering never takes a client offline.
- The activity log filters by subnet (--subnet, the Activity page,
  GET /events?subnet=).

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

internal/web/static/assets/pages/activity.js

@@ -2,16 +2,18 @@
 import { h, mount, input, select, debounce } from "../ui.js";
 import { get } from "../api.js";
 import { onLeave } from "../app.js";
+import { subnetLabel } from "../widgets.js";
 
 export async function render(el, params, query) {
-  const ifaces = await get("/interfaces");
+  const [ifaces, subnets] = await Promise.all([get("/interfaces"), get("/subnets")]);
+  const subnetSel = select([["", "all subnets"], ...subnets.map((s) => [String(s.id), subnetLabel(s)])], query.get("subnet") || "");
   const mac = input({ placeholder: "MAC address", value: query.get("mac") || "", class: "mono" });
   const iface = select([["", "all interfaces"], ...ifaces.filter((i) => i.subnets.length).map((i) => [i.name, i.name])], query.get("interface") || "");
   const out = h("div");
   let live = true;
   const pause = h("button", { onclick: () => { live = !live; pause.textContent = live ? "Pause" : "Resume"; } }, "Pause");
   const draw = async () => {
-    const evs = await get("/events", { mac: mac.value.trim(), interface: iface.value, limit: 300 });
+    const evs = await get("/events", { mac: mac.value.trim(), subnet: subnetSel.value, interface: iface.value, limit: 300 });
     mount(out, evs.length ? h("div", { class: "table-wrap" }, h("table", { class: "activity" },
       h("thead", null, h("tr", null, ["Time", "Interface", "Message", "Client", "Address", "Host name", ""].map((t) => h("th", null, t)))),
       h("tbody", null, evs.map((e) => {
@@ -26,14 +28,15 @@ export async function render(el, params, query) {
           h("td", { class: "mono" }, e.ip || ""),
           h("td", null, e.hostname || ""),
           h("td", { class: "detail" }, e.detail || ""));
-      })))) : h("div", { class: "empty" }, "No DHCP messages yet" + (mac.value || iface.value ? " that match." : ".")));
+      })))) : h("div", { class: "empty" }, "No DHCP messages yet" + (mac.value || subnetSel.value || iface.value ? " that match." : ".")));
   };
   mac.addEventListener("input", debounce(draw, 300));
+  subnetSel.addEventListener("change", draw);
   iface.addEventListener("change", draw);
   mount(el,
     h("div", { class: "page-head" }, h("div", { class: "grow" }, h("h1", null, "Activity"),
       h("div", { class: "muted" }, "The latest DHCP messages Steward received and sent, newest first. A MAC address leads to that client's leases; Only this follows just that client."))),
-    h("div", { class: "filter-row" }, mac, iface, pause),
+    h("div", { class: "filter-row" }, mac, subnetSel, iface, pause),
     h("div", { class: "panel" }, out));
   await draw();
   const t = setInterval(() => { if (live) draw().catch(() => {}); }, 3000);