feat(admin): per-unit live-monitoring (keepalive) toggle on /admin/slmm

Adds a "Live Monitoring (keepalive)" card listing each SLMM device with its
monitor_enabled state and an Enable/Disable toggle. Reads from /api/slmm/roster
(now includes monitor_enabled) and POSTs to /api/slmm/{unit}/monitor/{start,stop},
which persist the flag in SLMM (survives restarts; auto-started on boot). Shows a
reachability dot + 24/7 ON/OFF badge.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

templates/admin_slmm.html

@@ -42,6 +42,18 @@
     </div>
 </div>
 
+<!-- Live Monitoring (keepalive) -->
+<div class="rounded-xl bg-white dark:bg-slate-800 shadow-lg p-4 mb-6">
+    <h2 class="text-sm font-semibold text-gray-700 dark:text-gray-300 uppercase tracking-wider mb-1">Live Monitoring (keepalive)</h2>
+    <p class="text-xs text-gray-500 dark:text-gray-400 mb-3">
+        Keepalive runs the 1&nbsp;Hz DOD feed 24/7 (even with no viewer), which powers the live-chart
+        trail and continuous threshold alerts. Toggling persists and survives restarts.
+    </p>
+    <div id="monitor-list" class="text-sm">
+        <p class="text-gray-500 dark:text-gray-400">Loading…</p>
+    </div>
+</div>
+
 <!-- Raw API tester -->
 <div class="rounded-xl bg-white dark:bg-slate-800 shadow-lg p-4 mb-6">
     <h2 class="text-sm font-semibold text-gray-700 dark:text-gray-300 uppercase tracking-wider mb-3">Raw API Tester</h2>
@@ -132,7 +144,60 @@ async function sendRaw() {
     }
 }
 
+async function loadMonitors() {
+    const el = document.getElementById('monitor-list');
+    try {
+        const r = await fetch('/api/slmm/roster');
+        if (!r.ok) throw new Error('HTTP ' + r.status);
+        const d = await r.json();
+        const devices = d.devices || [];
+        if (!devices.length) {
+            el.innerHTML = '<p class="text-gray-500 dark:text-gray-400">No devices configured.</p>';
+            return;
+        }
+        el.innerHTML = devices.map(dev => {
+            const on = !!dev.monitor_enabled;
+            const reach = dev.status ? dev.status.is_reachable : null;
+            const reachDot = reach === false
+                ? '<span class="w-2 h-2 rounded-full bg-red-500 inline-block" title="unreachable"></span>'
+                : '<span class="w-2 h-2 rounded-full bg-green-500 inline-block" title="reachable"></span>';
+            return `
+            <div class="flex items-center justify-between border-b border-gray-100 dark:border-gray-700 py-2">
+                <div class="flex items-center gap-2">
+                    ${reachDot}
+                    <span class="font-mono text-gray-900 dark:text-white">${_esc(dev.unit_id)}</span>
+                    <span class="text-xs text-gray-500 dark:text-gray-400">${_esc(dev.host)}:${_esc(dev.tcp_port)}</span>
+                </div>
+                <div class="flex items-center gap-3">
+                    <span class="text-xs font-medium px-2 py-0.5 rounded ${on
+                        ? 'bg-green-100 text-green-700 dark:bg-green-900/40 dark:text-green-300'
+                        : 'bg-gray-100 text-gray-600 dark:bg-slate-700 dark:text-gray-400'}">${on ? '24/7 ON' : 'OFF'}</span>
+                    <button onclick="toggleMonitor('${_esc(dev.unit_id)}', ${!on})"
+                            class="px-3 py-1 text-xs rounded text-white ${on
+                                ? 'bg-red-600 hover:bg-red-700' : 'bg-seismo-orange hover:bg-orange-600'}">
+                        ${on ? 'Disable' : 'Enable'}
+                    </button>
+                </div>
+            </div>`;
+        }).join('');
+    } catch (e) {
+        el.innerHTML = `<p class="text-red-600 dark:text-red-400">Failed to load devices: ${_esc(e.message)}</p>`;
+    }
+}
+
+async function toggleMonitor(unitId, enable) {
+    const action = enable ? 'start' : 'stop';
+    try {
+        const r = await fetch(`/api/slmm/${encodeURIComponent(unitId)}/monitor/${action}`, { method: 'POST' });
+        if (!r.ok) throw new Error('HTTP ' + r.status);
+        await loadMonitors();
+    } catch (e) {
+        alert('Toggle failed: ' + e.message);
+    }
+}
+
 loadSlmmOverview();
-setInterval(loadSlmmOverview, 30000);
+loadMonitors();
+setInterval(() => { loadSlmmOverview(); loadMonitors(); }, 30000);
 </script>
 {% endblock %}