Add Copy comments as JSON control

[crintus]

Summary

• add a Copy control beside the existing comment export controls
• share the complete, import-compatible payload builder with Download
• reuse the existing copy icon, styling, toast, and clipboard fallback
• document the control and cover its clipboard payload with Playwright

Why

Reviewers can paste feedback directly into another tool without first downloading a JSON file. Download and Import remain unchanged.

Validation

• npm test - 456 tests passed across all configured browser and device projects
• git diff --check
• verified the four-control footer at 360 px without horizontal overflow