feat: add @codspeed/playwright package to bench electron apps

Introduce a @codspeed/playwright package exposing a Playwright-style
`bench(name, fn, options)` API. The benchmark function receives a
`{ page }` fixture mirroring Playwright's `test`, and a minimal options
argument carrying the number of rounds and Electron launch config.

Refs COD-2721
Co-Authored-By: Claude <noreply@anthropic.com>

Author: GuillaumeLagrange

packages/playwright/README.md

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+<div align="center">
+<h1><code>@codspeed/playwright</code></h1>
+
+[Playwright](https://playwright.dev) integration for [CodSpeed](https://codspeed.io), to benchmark [Electron](https://www.electronjs.org) apps end-to-end
+
+[![CI](https://github.com/CodSpeedHQ/codspeed-node/actions/workflows/ci.yml/badge.svg)](https://github.com/CodSpeedHQ/codspeed-node/actions/workflows/ci.yml)
+[![npm (scoped)](https://img.shields.io/npm/v/@codspeed/playwright)](https://www.npmjs.com/package/@codspeed/playwright)
+[![Discord](https://img.shields.io/badge/chat%20on-discord-7289da.svg)](https://discord.com/invite/MxpaCfKSqF)
+[![CodSpeed Badge](https://img.shields.io/endpoint?url=https://codspeed.io/badge.json)](https://codspeed.io/CodSpeedHQ/codspeed-node)
+
+</div>
+
+## Documentation
+
+Check out the [documentation](https://docs.codspeed.io/benchmarks/nodejs) for complete integration instructions.
+
+## Installation
+
+Install the plugin [`@codspeed/playwright`](https://www.npmjs.com/package/@codspeed/playwright) alongside `playwright` and your `electron` app dependency:
+
+```sh
+npm install --save-dev @codspeed/playwright playwright electron
+```
+
+or with `yarn`:
+
+```sh
+yarn add --dev @codspeed/playwright playwright electron
+```
+
+or with `pnpm`:
+
+```sh
+pnpm add --save-dev @codspeed/playwright playwright electron
+```
+
+## Usage
+
+This integration measures an Electron app driven through Playwright. Build your
+app first so the Electron main entrypoint exists (e.g. `out/main/index.js`),
+then write a benchmark with the `bench` function.
+
+`bench` launches the app once per round, drives it through the provided
+function, and reports the time spent inside that function to CodSpeed:
+
+```ts title="bench/inbox.bench.ts"
+import { bench } from "@codspeed/playwright";
+import path from "node:path";
+
+bench(
+  "inbox-search",
+  async ({ page }) => {
+    await page.fill("#search", "quarterly report");
+    await page.waitForSelector("#results");
+  },
+  {
+    appPath: path.resolve("out/main/index.js"),
+    // Bring the app to a steady state before each measured round (not measured).
+    setup: async ({ page }) => {
+      await page.waitForSelector("#main:not(.loading)");
+    },
+    rounds: 5,
+  },
+);
+```
+
+### Options
+
+| Option                   | Type                                  | Default             | Description                                                                               |
+| ------------------------ | ------------------------------------- | ------------------- | ----------------------------------------------------------------------------------------- |
+| `appPath`                | `string`                              | _(required)_        | Absolute path to the Electron main entrypoint (e.g. `out/main/index.js`).                 |
+| `rounds`                 | `number`                              | `1`                 | Number of measurement rounds. Overridable via the `CODSPEED_ROUNDS` environment variable. |
+| `electronArgs`           | `string[]`                            | `[]`                | Extra CLI flags forwarded to Electron.                                                    |
+| `cwd`                    | `string`                              | `process.cwd()`     | Working directory for the Electron process. Also where `electron` is resolved from.       |
+| `electronExecutablePath` | `string`                              | resolved `electron` | Absolute path to the Electron binary. Set only to override the default resolution.        |
+| `setup`                  | `({ page }) => void \| Promise<void>` | —                   | Runs before each round, after the window opens. Not measured.                             |
+| `teardown`               | `({ page }) => void \| Promise<void>` | —                   | Runs after each round, before the app closes. Not measured.                               |
+
+The function receives a Playwright [`Page`](https://playwright.dev/docs/api/class-page) for the Electron window as `page`.
+
+## Running the benchmarks
+
+Run your benchmark file with Node (or `tsx` for TypeScript):
+
+```bash
+$ node bench/inbox.bench.ts
+[CodSpeed] [round 1/5] 42.13 ms
+...
+```
+
+Locally this simply runs the app and prints per-round timings. Instrumentation
+and uploads to CodSpeed only happen in the
+[CI environment](https://docs.codspeed.io/benchmarks/nodejs#running-the-benchmarks-in-your-ci),
+where the CodSpeed runner picks up the results.

packages/playwright/package.json

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+{
+  "name": "@codspeed/playwright",
+  "version": "5.4.0",
+  "description": "Playwright benchmarking integration for CodSpeed",
+  "keywords": [
+    "codspeed",
+    "benchmark",
+    "playwright",
+    "electron",
+    "performance"
+  ],
+  "main": "dist/index.cjs",
+  "module": "dist/index.es5.js",
+  "types": "dist/index.d.ts",
+  "type": "module",
+  "exports": {
+    "types": "./dist/index.d.ts",
+    "import": "./dist/index.es5.js",
+    "require": "./dist/index.cjs"
+  },
+  "files": [
+    "dist"
+  ],
+  "scripts": {
+    "build": "NODE_NO_WARNINGS=1 rollup -c rollup.config.ts --configPlugin typescript",
+    "test": "echo 'no tests'",
+    "test/integ": "echo 'no integ tests'",
+    "lint": "eslint .",
+    "typecheck": "tsc --noEmit --pretty",
+    "format": "prettier --config ../../.prettierrc.json --ignore-path ../../.prettierignore --check .",
+    "fix-format": "prettier --config ../../.prettierrc.json --ignore-path ../../.prettierignore --write .",
+    "clean": "rm -rf dist"
+  },
+  "author": "Guillaume Lagrange <guillaume@codspeed.io>",
+  "repository": "https://github.com/CodSpeedHQ/codspeed-node",
+  "homepage": "https://codspeed.io",
+  "license": "Apache-2.0",
+  "devDependencies": {
+    "playwright": "^1.48.0",
+    "playwright-core": "^1.48.0",
+    "vitest": "^3.2.4"
+  },
+  "dependencies": {
+    "@codspeed/core": "workspace:^5.4.0"
+  },
+  "peerDependencies": {
+    "playwright": ">=1.40.0"
+  }
+}

packages/playwright/rollup.config.ts

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+import { defineConfig } from "rollup";
+import { declarationsPlugin, jsPlugins } from "../../rollup.options";
+import pkg from "./package.json" assert { type: "json" };
+
+const entrypoint = "src/index.ts";
+
+export default defineConfig([
+  {
+    input: entrypoint,
+    output: [
+      {
+        file: pkg.types,
+        format: "es",
+        sourcemap: true,
+      },
+    ],
+    plugins: declarationsPlugin({ compilerOptions: { composite: false } }),
+  },
+  {
+    input: entrypoint,
+    output: [
+      {
+        file: pkg.main,
+        format: "cjs",
+        sourcemap: true,
+      },
+      { file: pkg.module, format: "es", sourcemap: true },
+    ],
+    plugins: jsPlugins(pkg.version),
+    external: ["@codspeed/core", "playwright", "playwright-core"],
+  },
+]);