test(desktop): Playwright electron e2e harness

Launches the built app (out/main/index.js) via Playwright's _electron
API — no browser project, no chromium download. Adds a launch fixture
(electronApp/window/app), an AppPage page object with a screenshot
helper for autonomous visual review, and a boot smoke suite (shell
renders, @commitea/core label-parse runs in the renderer, preload API
exposed). Scripts: e2e (build+run), e2e:only, e2e:report. Artifacts
gitignored.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/desktop/playwright.config.ts

@@ -0,0 +1,26 @@
+import { defineConfig } from '@playwright/test'
+
+/**
+ * E2E harness for the Electron app. Tests launch the *built* app
+ * (`out/main/index.js`) through Playwright's `_electron` API — see
+ * `e2e/fixtures.ts`. There is no browser project and no chromium download:
+ * `_electron` drives the app's own bundled electron.
+ *
+ * Run `yarn e2e` (builds first) for a fresh run, or `yarn e2e:only` to reuse
+ * the existing `out/` build during a tight iteration loop.
+ */
+export default defineConfig({
+  testDir: './e2e',
+  outputDir: './e2e/.artifacts/test-results',
+  fullyParallel: false,
+  workers: 1, // one electron instance at a time — deterministic, avoids window races
+  forbidOnly: !!process.env.CI,
+  retries: 0,
+  timeout: 30_000,
+  expect: { timeout: 5_000 },
+  reporter: [['list'], ['html', { outputFolder: './e2e/.artifacts/report', open: 'never' }]],
+  use: {
+    trace: 'retain-on-failure',
+    screenshot: 'only-on-failure',
+  },
+})