Add a "review mode"

[carlos-zamora]

Describe the feature or problem you'd like to solve

Reviewing PRs or even the changes made by copilot can be a long and difficult process, especially with more code being generated by AI tools.

Proposed solution

Currently, shift+tab cycles modes like "plan mode". I propose a new "review mode" with the following:

• do NOT allow modifications to the product code
• prefer referring to new changes over full architecture (or how they relate to the full architecture)
• detect code-health issues like const in C++, whitespace, etc. Try to match the mannerisms used in the same files. (i.e. function comments?)
• if possible, identify tests to run and provide feedback on that. Should more tests be added? Do the tests pass? Do the tests need to be updated?
• if possible, refer to the actual PR on GitHub. Consider relevant comments in the code area under review. (advanced feature: look at other PRs or recent changes in similar areas, just to be aware of them)

Example prompts or workflows

No response

Additional context

VS Code lets you look at GitHub PRs. You can see what changes there are, but also have access to AI tooling. I use this all the time to ask questions about the new implementation or how it fits into the larger architecture.

Thinking about how to have a similar experience in the copilot cli would be helpful.