fix: broadcast k6 stdout summary and show full stats

- Remove --out json=- (was flooding stdout and hiding summary)
- Broadcast both stdout (summary table) and stderr (live warnings)
- Add --summary-trend-stats with p(90)/p(95)/p(99)
- Parse checks, failed count/total, data received, all percentiles
- Strip ANSI codes before regex matching
- Add threshold pass/fail banner with per-threshold status
- Show all duration percentiles as individual cards

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

frontend/style.css

@@ -150,10 +150,25 @@ textarea { font-family: var(--mono); resize: vertical; }
   color: #a5f3fc;
 }
 
+/* THRESHOLD BANNER */
+.threshold-banner {
+  border-radius: 8px;
+  padding: .85rem 1rem;
+  margin-bottom: 1rem;
+  border: 1px solid;
+}
+.threshold-banner.pass { background: rgba(34,197,94,.08);  border-color: rgba(34,197,94,.3);  color: var(--green); }
+.threshold-banner.fail { background: rgba(239,68,68,.08);  border-color: rgba(239,68,68,.3);  color: var(--red); }
+.threshold-banner ul { list-style: none; margin-top: .4rem; padding: 0; }
+.threshold-banner li { font-size: .85rem; padding: .15rem 0; font-family: var(--mono); }
+.threshold-banner li.pass { color: var(--green); }
+.threshold-banner li.fail { color: var(--red); }
+
 /* SUMMARY CARDS */
+#summary-cards { margin-top: .5rem; }
 .summary-grid {
   display: grid;
-  grid-template-columns: repeat(auto-fill, minmax(180px, 1fr));
+  grid-template-columns: repeat(auto-fill, minmax(170px, 1fr));
   gap: 1rem;
   margin-top: .75rem;
 }