First cut at a CoPilot review agent (#12889)

* First cut at a CoPilot review agent

* Update .github/copilot-instructions.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update .github/instructions/HRW.instructions.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update .github/instructions/HRW.instructions.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update .github/copilot-instructions.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* More review changes

Note that as far as I can figure, CoPilot does not support loading another
file via e.g. @.claude/CLAUDE.md etc., so there will be a little bit of
duplication here I think.

* Update .github/copilot-instructions.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* More review changes

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Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: zwoop