feat: live timing waterfall with TTFB, DNS, TLS, TCP, sending, receiving

Backend:
- Track all k6 HTTP phase metrics via PHASE_MAP in ingestPoint:
  http_req_blocked (DNS+wait), http_req_connecting, http_req_tls_handshaking,
  http_req_sending, http_req_waiting (TTFB), http_req_receiving
- Compute avg + p95 per phase in computeLiveMetrics, broadcast every second
- parseSummary now captures all trend metrics with generic trendRe()

Frontend:
- Live waterfall bar chart updates every second during the test
- Each phase has a distinct colour: indigo/sky/purple/emerald/amber/blue
- Bar width = phase avg as % of total request time
- TTFB p95 + p99 shown below the waterfall
- Bars animate smoothly with CSS transitions
- Waterfall resets cleanly on new test start

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

frontend/style.css

@@ -307,6 +307,64 @@ textarea { font-family: var(--mono); resize: vertical; }
   letter-spacing: .05em;
 }
 
+/* ── TIMING WATERFALL ───────────────────────────────────────────────────────── */
+.waterfall-wrap {
+  margin-top: .75rem;
+  border-top: 1px solid var(--border);
+  padding-top: .9rem;
+}
+.waterfall-title {
+  font-size: .78rem;
+  font-weight: 600;
+  color: var(--muted);
+  text-transform: uppercase;
+  letter-spacing: .06em;
+  margin-bottom: .6rem;
+}
+.wf-hint { font-weight: 400; text-transform: none; letter-spacing: 0; }
+
+.wf-row {
+  display: grid;
+  grid-template-columns: 120px 1fr 70px;
+  align-items: center;
+  gap: .5rem;
+  margin-bottom: .35rem;
+}
+.wf-label { font-size: .78rem; color: var(--muted); white-space: nowrap; }
+.wf-bar-wrap {
+  background: var(--border);
+  border-radius: 999px;
+  height: 8px;
+  overflow: hidden;
+}
+.wf-bar {
+  height: 100%;
+  border-radius: 999px;
+  width: 0%;
+  transition: width .6s cubic-bezier(.4,0,.2,1);
+}
+.wf-val { font-size: .78rem; font-family: var(--mono); color: var(--text); text-align: right; }
+
+/* Phase colours */
+.wf-blocked    { background: #818cf8; } /* indigo  — DNS/blocked */
+.wf-connecting { background: #38bdf8; } /* sky     — TCP connect */
+.wf-tls        { background: #a78bfa; } /* purple  — TLS */
+.wf-sending    { background: #34d399; } /* emerald — sending */
+.wf-ttfb       { background: #f59e0b; } /* amber   — TTFB (most important) */
+.wf-receiving  { background: #60a5fa; } /* blue    — receiving */
+
+.wf-p95-row {
+  display: flex;
+  align-items: center;
+  gap: .5rem;
+  margin-top: .4rem;
+  padding-top: .4rem;
+  border-top: 1px dashed var(--border);
+  flex-wrap: wrap;
+}
+.wf-p95-label { font-size: .72rem; color: var(--muted); }
+.wf-p95-val   { font-size: .85rem; font-weight: 700; font-family: var(--mono); color: var(--yellow); }
+
 /* ── BANDWIDTH ROW ──────────────────────────────────────────────────────────── */
 .bw-row {
   display: flex;