feat: expand CDP perf metrics — add DOM nodes, script duration, event listeners (#9887)

## Summary

Expands the performance testing infrastructure to collect 4 additional
CDP metrics that are already returned by `Performance.getMetrics` but
were not being read. This is a zero-cost expansion — no additional CDP
calls, just reading more fields from the existing response.

## New Metrics

| Metric | CDP Source | What It Detects |
|---|---|---|
| `domNodes` | `Nodes` | DOM node count delta — widget DOM leaks during
node create/destroy |
| `jsHeapTotalBytes` | `JSHeapTotalSize` | Total heap delta — combined
with `heapDeltaBytes` shows GC pressure |
| `scriptDurationMs` | `ScriptDuration` | JS execution time vs total
task time — script vs rendering balance |
| `eventListeners` | `JSEventListeners` | Listener count delta — detects
listener accumulation across lifecycle |

## Changes

### `browser_tests/fixtures/helpers/PerformanceHelper.ts`
- Added 4 fields to `PerfSnapshot` interface
- Added 4 fields to `PerfMeasurement` interface
- Wired through `getSnapshot()` and `stopMeasuring()`

### `scripts/perf-report.ts`
- Added 4 fields to `PerfMeasurement` interface
- Expanded `MetricKey` type and `REPORTED_METRICS` array with 3 new
reported metrics (`domNodes`, `scriptDurationMs`, `eventListeners`)
- `jsHeapTotalBytes` is collected but not in `REPORTED_METRICS` — it's
used alongside `heapDeltaBytes` for GC pressure ratio analysis

## Why These 4

From a gap analysis of all ~30 CDP metrics, these were identified as
highest priority for ComfyUI:
- **`Nodes`** (P0): ComfyUI dynamically creates/destroys widget DOM. DOM
bloat from leaked widgets is a key performance risk, especially for Vue
Nodes 2.0.
- **`ScriptDuration`** (P1): Separates JS execution from layout/paint.
Reveals whether perf issues are script-heavy or rendering-heavy.
- **`JSEventListeners`** (P1): Widget lifecycle can leak listeners
across node add/remove cycles.
- **`JSHeapTotalSize`** (P1): With `JSHeapUsedSize`, the ratio shows GC
fragmentation pressure.

## Backward Compatibility

The `PerfMeasurement` interface is extended (not changed). Old baseline
`perf-metrics.json` files without these fields will have `undefined`
values, which the report script handles gracefully (shows `—` for
missing data).

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9887-feat-expand-CDP-perf-metrics-add-DOM-nodes-script-duration-event-listeners-3226d73d3650818abea1d4a441667c38)
by [Unito](https://www.unito.io)

---------

Co-authored-by: GitHub Action <action@github.com>
Co-authored-by: Alexander Brown <drjkl@comfy.org>

browser_tests/fixtures/helpers/PerformanceHelper.ts

@@ -8,6 +8,10 @@ interface PerfSnapshot {
   TaskDuration: number
   JSHeapUsedSize: number
   Timestamp: number
+  Nodes: number
+  JSHeapTotalSize: number
+  ScriptDuration: number
+  JSEventListeners: number
 }
 
 export interface PerfMeasurement {
@@ -19,6 +23,10 @@ export interface PerfMeasurement {
   layoutDurationMs: number
   taskDurationMs: number
   heapDeltaBytes: number
+  domNodes: number
+  jsHeapTotalBytes: number
+  scriptDurationMs: number
+  eventListeners: number
 }
 
 export class PerformanceHelper {
@@ -59,7 +67,11 @@ export class PerformanceHelper {
       LayoutDuration: get('LayoutDuration'),
       TaskDuration: get('TaskDuration'),
       JSHeapUsedSize: get('JSHeapUsedSize'),
-      Timestamp: get('Timestamp')
+      Timestamp: get('Timestamp'),
+      Nodes: get('Nodes'),
+      JSHeapTotalSize: get('JSHeapTotalSize'),
+      ScriptDuration: get('ScriptDuration'),
+      JSEventListeners: get('JSEventListeners')
     }
   }
 
@@ -90,7 +102,11 @@ export class PerformanceHelper {
       layouts: delta('LayoutCount'),
       layoutDurationMs: delta('LayoutDuration') * 1000,
       taskDurationMs: delta('TaskDuration') * 1000,
-      heapDeltaBytes: delta('JSHeapUsedSize')
+      heapDeltaBytes: delta('JSHeapUsedSize'),
+      domNodes: delta('Nodes'),
+      jsHeapTotalBytes: delta('JSHeapTotalSize'),
+      scriptDurationMs: delta('ScriptDuration') * 1000,
+      eventListeners: delta('JSEventListeners')
     }
   }
 }