feat: add test scenario feedback command

[jy-tan]

Summary

Add tusk unit feedback so users and agents can submit structured feedback for generated test scenarios directly from the CLI.

Changes

• Add a new tusk unit feedback command that accepts JSON from a file or stdin and submits feedback for multiple scenarios in one call
• Extend the shared unit API client to support JSON requests with request bodies and add a feedback submission method
• Document the feedback workflow in tusk unit overview help and add detailed command help with payload examples, allowed feedback values, and heredoc usage
• Keep the CLI-facing payload user-oriented by using positive_feedback / negative_feedback and applied_locally, rather than exposing backend-oriented fields

[cubic-dev-ai]

No issues found across 3 files