feat: add Playwright e2e tests for onboarding wizard flow

Scaffolds end-to-end testing with Playwright for the onboarding wizard.
Runs in skip_llm mode by default (UI-only, no LLM costs). Set
PAPERCLIP_E2E_SKIP_LLM=false for full heartbeat verification.

- tests/e2e/playwright.config.ts: Playwright config with webServer
- tests/e2e/onboarding.spec.ts: 4-step wizard flow test
- .github/workflows/e2e.yml: manual workflow_dispatch CI workflow
- package.json: test:e2e and test:e2e:headed scripts

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -25,10 +25,13 @@
     "docs:dev": "cd docs && npx mintlify dev",
     "smoke:openclaw-join": "./scripts/smoke/openclaw-join.sh",
     "smoke:openclaw-docker-ui": "./scripts/smoke/openclaw-docker-ui.sh",
-    "smoke:openclaw-sse-standalone": "./scripts/smoke/openclaw-sse-standalone.sh"
+    "smoke:openclaw-sse-standalone": "./scripts/smoke/openclaw-sse-standalone.sh",
+    "test:e2e": "npx playwright test --config tests/e2e/playwright.config.ts",
+    "test:e2e:headed": "npx playwright test --config tests/e2e/playwright.config.ts --headed"
   },
   "devDependencies": {
     "@changesets/cli": "^2.30.0",
+    "@playwright/test": "^1.58.2",
     "esbuild": "^0.27.3",
     "typescript": "^5.7.3",
     "vitest": "^3.0.5"