feat: add playwright integration feature

[miinhho]

Summary

New @memlab/playwright package — a Playwright fixture that attaches memlab's leak detection to existing Playwright tests by destructuring a memlab parameter. No scenario rewrite, no Puppeteer dependency.

import {test, expect} from '@memlab/playwright';

test('modal close does not leak', async ({page, memlab}) => {
  await page.goto('/');
  await memlab.baseline();
  await page.click('text=Open');
  await page.click('text=Close');
  await memlab.expectNoLeaks();
});

Motivation

memlab's existing APIs (@memlab/api, memlab run) drive the browser through a Puppeteer-based scenario runner. Teams already running Playwright e2e suites can't attach leak detection without rewriting their specs. This package bridges the gap by piggybacking on the user's existing page via a CDP session.

Design notes

• Chromium only. Heap snapshots go over CDP, which Playwright only exposes for Chromium. On Firefox / WebKit the fixture becomes a no-op: the test still runs, no leak detection, a memlab-skip annotation is attached. README calls this out.
• Opt-in per test. Fixture setup runs only when memlab is destructured. Tests that don't use it pay no overhead
• 3-phase snapshot (baseline / target / final) wired to fixture lifecycle. forceFullGC via HeapProfiler.collectGarbage CDP, no --expose-gc flag required.
• Configurable. memlab.configure({gc, leakFilter}) for per-project GC tuning and custom filters. Merge semantics preserve prior fields.
• CI-friendly failure output. formatLeakMessage picks the $memLabTag:leaked hop (not the Window root), strips memlab-internal $tabsOrder metadata from attached JSON, and heap snapshots only attach when leaks are detected (skips ~13 MB per clean test).

API

• memlab.baseline(): Capture baseline heap snapshot
• memlab.target() / memlab.final(): Manual phase control
• memlab.configure({gc?, leakFilter?}): Per-test tuning
• memlab.findLeaks(): Returns ISerializedInfo[] | null
• memlab.expectNoLeaks(): Hard assertion with triage-friendly error

If neither findLeaks nor expectNoLeaks is called, the fixture auto-captures missing phases and soft-asserts no leaks during teardown.