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>

app.py

@@ -130,6 +130,7 @@ def index():
     last_check = db.get_state('last_check', 'Never')
     snapshot = json.loads(snapshot_raw) if snapshot_raw else {}
     suppressions = db.get_active_suppressions()
+    recent_resolved = db.get_recent_resolved(hours=24, limit=10)
     return render_template(
         'index.html',
         user=user,
@@ -138,6 +139,7 @@ def index():
         snapshot=snapshot,
         last_check=last_check,
         suppressions=suppressions,
+        recent_resolved=recent_resolved,
     )