feat: add GitHub Copilot CLI plugin

[Siddhant-K-code]

Summary

• package the repository as an agent-strace Copilot CLI plugin with a marketplace catalog
• add native Copilot lifecycle hooks, a trace analyst agent, and an investigation skill
• align generated hooks and payload normalization with the current GitHub hook format
• preserve existing trace metadata when Copilot sessions resume
• document marketplace installation and bump the feature version to 0.94.0

Validation

• installed and listed the plugin through a clean local marketplace with Copilot CLI 1.0.80
• passed focused hook and plugin tests on Python 3.13 (41 tests)
• git diff --check

The complete suite currently also reports 4 failures and 17 errors in existing assignment/compliance tests on macOS because their path-safety checks reject the /var symlink; those modules are not changed here.

Official format: https://docs.github.com/en/copilot/how-tos/copilot-cli/customize-copilot/plugins-creating