feat: link health summary, recently resolved panel, event duration

- dashboard: pass recent_resolved (last 24h, limit 10) to index template;
  render "Recently Resolved" section showing type, target, resolved time,
  and calculated duration (first_seen → resolved_at)
- dashboard: event-age spans now also update via setInterval; duration
  shown for resolved events (e.g. "2h 15m")
- links page: link health summary panel shows server iface count,
  error/flap counts, switch port up/down, PoE total draw/capacity bar;
  only shows problematic stats if non-zero; shows "All OK ✔" when clean
- style.css: new classes for summary panel, resolved row/badge

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

static/style.css

@@ -1524,3 +1524,73 @@ a:hover { text-decoration: underline; text-shadow: var(--glow-amber); }
   border-radius: 2px;
   font-size: .88em;
 }
+
+/* ── Link health summary panel ────────────────────────────────────── */
+.link-summary-panel {
+  background: var(--bg2);
+  border: 1px solid var(--border);
+  border-radius: 2px;
+  padding: 12px 16px;
+  margin-bottom: 12px;
+}
+
+.link-summary-panel.link-summary-has-alerts {
+  border-color: var(--amber);
+}
+
+.link-summary-grid {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 20px;
+  align-items: flex-end;
+}
+
+.link-summary-stat {
+  min-width: 80px;
+}
+
+.link-summary-stat.lss-alert .lss-label {
+  color: var(--amber);
+}
+
+.lss-label {
+  display: block;
+  font-size: .62em;
+  color: var(--text-muted);
+  text-transform: uppercase;
+  letter-spacing: .05em;
+  margin-bottom: 2px;
+}
+
+.lss-value {
+  font-size: 1.2em;
+  font-weight: bold;
+  color: var(--text);
+}
+
+.lss-sub {
+  font-size: .7em;
+  color: var(--text-muted);
+  font-weight: normal;
+}
+
+/* ── Recently resolved table ──────────────────────────────────────── */
+.row-resolved td {
+  opacity: 0.75;
+}
+
+.badge-resolved {
+  background: var(--bg3);
+  color: var(--text-muted);
+  border-color: var(--border);
+  text-decoration: line-through;
+}
+
+.section-badge-resolved {
+  background: var(--bg3);
+  color: var(--text-muted);
+  border: 1px solid var(--border);
+  font-size: .65em;
+  padding: 2px 7px;
+  border-radius: 10px;
+}