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/index.html

@@ -154,7 +154,7 @@
 
           </div>
 
-          <!-- Live stat strip -->
+          <!-- Live stat strip — response times -->
           <div class="stats-strip" id="stats-strip">
             <div class="stat-cell" id="sc-reqs">
               <span class="sc-val">--</span><span class="sc-lbl">Requests</span>
@@ -163,7 +163,7 @@
               <span class="sc-val">--</span><span class="sc-lbl">Req / s</span>
             </div>
             <div class="stat-cell" id="sc-avg">
-              <span class="sc-val">--</span><span class="sc-lbl">Avg</span>
+              <span class="sc-val">--</span><span class="sc-lbl">Avg total</span>
             </div>
             <div class="stat-cell" id="sc-p90">
               <span class="sc-val">--</span><span class="sc-lbl">p(90)</span>
@@ -176,6 +176,49 @@
             </div>
           </div>
 
+          <!-- Live timing phases waterfall -->
+          <div class="waterfall-wrap" id="waterfall-wrap">
+            <div class="waterfall-title">Request timing breakdown <span class="wf-hint">(avg per phase)</span></div>
+            <div class="waterfall" id="waterfall">
+              <div class="wf-row" id="wf-blocked">
+                <span class="wf-label">DNS / Blocked</span>
+                <div class="wf-bar-wrap"><div class="wf-bar wf-blocked"></div></div>
+                <span class="wf-val">--</span>
+              </div>
+              <div class="wf-row" id="wf-connecting">
+                <span class="wf-label">TCP connect</span>
+                <div class="wf-bar-wrap"><div class="wf-bar wf-connecting"></div></div>
+                <span class="wf-val">--</span>
+              </div>
+              <div class="wf-row" id="wf-tls">
+                <span class="wf-label">TLS handshake</span>
+                <div class="wf-bar-wrap"><div class="wf-bar wf-tls"></div></div>
+                <span class="wf-val">--</span>
+              </div>
+              <div class="wf-row" id="wf-sending">
+                <span class="wf-label">Sending</span>
+                <div class="wf-bar-wrap"><div class="wf-bar wf-sending"></div></div>
+                <span class="wf-val">--</span>
+              </div>
+              <div class="wf-row" id="wf-ttfb">
+                <span class="wf-label">TTFB (waiting)</span>
+                <div class="wf-bar-wrap"><div class="wf-bar wf-ttfb"></div></div>
+                <span class="wf-val">--</span>
+              </div>
+              <div class="wf-row" id="wf-receiving">
+                <span class="wf-label">Receiving</span>
+                <div class="wf-bar-wrap"><div class="wf-bar wf-receiving"></div></div>
+                <span class="wf-val">--</span>
+              </div>
+            </div>
+            <div class="wf-p95-row" id="wf-p95-row" style="display:none">
+              <span class="wf-p95-label">TTFB p(95)</span>
+              <span class="wf-p95-val" id="wf-ttfb-p95">--</span>
+              <span class="wf-p95-label" style="margin-left:1rem">TTFB p(99)</span>
+              <span class="wf-p95-val" id="wf-ttfb-p99">--</span>
+            </div>
+          </div>
+
           <!-- Bandwidth row -->
           <div class="bw-row" id="bw-row">
             <div class="bw-item">