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>

.github/workflows/e2e.yml

@@ -0,0 +1,44 @@
+name: E2E Tests
+
+on:
+  workflow_dispatch:
+    inputs:
+      skip_llm:
+        description: "Skip LLM-dependent assertions (default: true)"
+        type: boolean
+        default: true
+
+jobs:
+  e2e:
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    env:
+      PAPERCLIP_E2E_SKIP_LLM: ${{ inputs.skip_llm && 'true' || 'false' }}
+      ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: pnpm/action-setup@v4
+        with:
+          version: 9
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: pnpm
+
+      - run: pnpm install --frozen-lockfile
+      - run: pnpm build
+      - run: npx playwright install --with-deps chromium
+
+      - name: Run e2e tests
+        run: pnpm run test:e2e
+
+      - uses: actions/upload-artifact@v4
+        if: always()
+        with:
+          name: playwright-report
+          path: |
+            tests/e2e/playwright-report/
+            tests/e2e/test-results/
+          retention-days: 14