docs(ai): improve onboarding steps (onboarding-audit-agent)

Added missing `npx playwright install` step to README.md and CONTRIBUTING.md to ensure smoke tests pass in a fresh environment.
Added completion log for onboarding-audit-agent.

Co-authored-by: PR0M3TH3AN <[email protected]>

CONTRIBUTING.md

@@ -105,6 +105,12 @@ To set up the project locally:
    npm ci
    ```
 
+   If you plan to run smoke tests or visual tests, install the Playwright browsers:
+
+   ```bash
+   npx playwright install
+   ```
+
 3. **Start the Application**:
 
    ```bash