tests: end to end tests and documents

[dhl123]

Summary

• Finished end to end tests.
• Update the root README to point new users to the HR agent as a start. Revise the READMEs for all five examples; the employee and HR agent guides now cover testing test generation in update mode.
• Made minor changes to four skill files with guidance for policy creation, policy cross-validation, and Promptfoo test generation.
• Refresh example guidance, tool definitions, Promptfoo configurations, policies, and saved test cases.
• Update .env_template to use the HR agent and Promptfoo as the example defaults.
• Add scripts/clean.sh back to clear generated reference and ARES files and reset the working policy.
• Update examples/hr-agent/agent.py to handle model provider prefixes.

Checks

• make ci passes (lint, Rego lint, license headers, build smoke)
• make test passes (policy scorecard — needed if policy behavior changed)
• CHANGELOG.md updated under ## [Unreleased] (if user-facing)
• PR title uses a conventional prefix (feat:, fix:, test:, docs:, chore:, or refactor:)
• Commits are signed off for the DCO (git commit -s)

Notes (optional)

Design sketch, screenshots, or extra context.