feat: add Playwright E2E smoke tests

Follows the pattern established in headlamp-intel-gpu-plugin (PR #25):
- e2e/sealed-secrets.spec.ts: 5 smoke tests covering sidebar navigation,
  list view, sealing keys view, cross-view navigation, and plugin settings
- e2e/auth.setup.ts: shared OIDC + token auth setup
- playwright.config.ts: fail-fast if HEADLAMP_URL not set (no prod URL fallback)
- scripts/deploy-e2e-headlamp.sh: ConfigMap-based plugin injection to privilegedescalation-dev
- scripts/teardown-e2e-headlamp.sh: clean teardown of all E2E resources

package.json

@@ -29,6 +29,8 @@
     "format:check": "prettier --check src/",
     "test": "vitest run",
     "test:watch": "vitest",
+    "e2e": "playwright test",
+    "e2e:headed": "playwright test --headed",
     "storybook": "headlamp-plugin storybook",
     "storybook-build": "headlamp-plugin storybook-build",
     "i18n": "headlamp-plugin i18n",
@@ -56,6 +58,7 @@
   },
   "devDependencies": {
     "@headlamp-k8s/eslint-config": "^0.6.0",
+    "@playwright/test": "^1.58.2",
     "@iconify/react": "^6.0.2",
     "@kinvolk/headlamp-plugin": "^0.13.0",
     "@mui/material": "^5.15.14",