Version 0.3.8 - use new execution task API + UX upgrades

[aliroberts]

Release - 0.3.8

Update weco-cli to use new execution task API + UX upgrades

Summary

This PR migrates weco-cli to the new execution task API and removes the legacy flow, while improving the interactive UX and run lifecycle handling.

Key changes

• API migration
  • Switch to the new execution task API
  • Use updated task API responses that include run data
  • Remove the legacy flow
• CLI / UX improvements
  • Add rich UI for a better interactive experience
  • Ensure the best metric value is shown in the resume display
  • Add automatic browser opening where appropriate
  • Add filename validation and improve interrupt handling (cleaner shutdown)
  • Stop the heartbeat when a run completes
• New commands / flags
  • Add login command
  • Add run --require-review option

Why

• Align weco-cli with the new task execution model and data shape.
• Improve reliability and polish around run lifecycle, shutdown, and display correctness.