chore(actions): clarify workflow names and remove unused e2e jobs

[TsuyoshiUshio]

Summary

• Rename the main CI workflow from Build Plugins to Build and Test.
• Rename Vally workflows to purpose-oriented names:
  • Skill Evaluation - Offline for non-Azure-deploying evals.
  • Skill Evaluation - Azure Live Deploy for evals that deploy real Azure resources.
  • Cleanup Azure Live Eval Resources for the Azure cleanup safety net.
• Remove obsolete workflows:
  • Nightly E2E Tests (not wired with required agent CLIs and no recent runs).
  • Skill Evaluation - Live Azure Login Smoke (superseded by Azure Live Deploy validation).
• Update eval documentation and workflow links to match the new names.

Validation

• npm run eval:lint
• Parsed all workflow and eval YAML files with the repo's yaml parser