[Feature request]: Github Copilot Hooks

[r1bilski]

Github Copilot has support for hooks as well: https://docs.github.com/en/copilot/concepts/agents/coding-agent/about-hooks

Two things to consider are:

• Copilot has no support for "Prompt" type hooks (I already refactored the code to handle that case in feat: implement opencode hooks #1001)
• Copilot allows for declaring powershell or bash scripts for each hook. We'd need to make a decision on how to handle that.

Some of the refactorings in #1001 like removing the assumption that the only two implementations are Claude and Cursor would also be useful to have in for this.

@dyoshikawa I'd be happy to implement this if you provide your input on the two considerations above, and whether we want to tackle this before #1001 is merged (causing conflicts) or after.

[cm-dyoshikawa]

@cm-dyoshikawa Looks very good! Anyway, I assigned you to this issue.