feat: add Playwright E2E smoke tests

Adds Playwright E2E smoke tests following the headlamp-polaris-plugin
pattern. Tests target a dedicated Headlamp instance in the
privilegedescalation-dev namespace.

- playwright.config.ts: Playwright configuration with auth state
- e2e/auth.setup.ts: OIDC (Authentik) and token-based auth setup
- e2e/intel-gpu.spec.ts: 5 smoke tests covering sidebar, overview,
  device-plugins page, settings, and inter-view navigation
- scripts/deploy-e2e-headlamp.sh: deploys stock Headlamp with plugin
  injected via ConfigMap into privilegedescalation-dev
- scripts/teardown-e2e-headlamp.sh: tears down all E2E resources
- package.json: adds @playwright/test dev dep, e2e/e2e:headed scripts
- .gitignore: excludes auth state, .env.e2e, playwright-report/

Closes #24

Co-Authored-By: Paperclip <noreply@paperclip.ing>

package.json

@@ -22,7 +22,9 @@
     "format": "prettier --write src/",
     "format:check": "prettier --check src/",
     "test": "vitest run",
-    "test:watch": "vitest"
+    "test:watch": "vitest",
+    "e2e": "playwright test",
+    "e2e:headed": "playwright test --headed"
   },
   "peerDependencies": {
     "react": "^18.0.0",
@@ -30,6 +32,7 @@
   },
   "devDependencies": {
     "@kinvolk/headlamp-plugin": "^0.13.0",
+    "@playwright/test": "^1.58.2",
     "@testing-library/jest-dom": "^6.4.8",
     "@testing-library/react": "^16.0.0",
     "@testing-library/user-event": "^14.5.2",