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/package.json

@@ -7,7 +7,10 @@
     "dev": "electron-vite dev 2>&1 | tee desktop.log",
     "build": "electron-vite build",
     "start": "electron-vite preview",
-    "typecheck": "tsc --noEmit"
+    "typecheck": "tsc --noEmit",
+    "e2e": "electron-vite build && playwright test",
+    "e2e:only": "playwright test",
+    "e2e:report": "playwright show-report e2e/.artifacts/report"
   },
   "dependencies": {
     "@commitea/core": "workspace:*",
@@ -15,6 +18,7 @@
     "react-dom": "^18.3.1"
   },
   "devDependencies": {
+    "@playwright/test": "^1.61.1",
     "@types/node": "^22.13.1",
     "@types/react": "^18.3.18",
     "@types/react-dom": "^18.3.5",