Feature: /review slash command for automated code review

[karthiknish]

Add a /review slash command that triggers a structured code review of the current changes or conversation output similar to codex.

[theoneand33]

or you could create/download some code review skill then use $review

[acidoxee]

I'd use this a lot if it could be embedded in T3 Code itself, since using outside tools always breaks the flow. Other tools doing something similar: codiff (LLM walkthroughs), godiff (groups files by intent using a locally installed agent), and Linear's PR review guides, which inspired pulls.review.

A few suggestions:

1. Don't limit it to PRs. Most diffs I review in T3 Code are turn or branch diffs an agent just wrote. The grouped view would be just as useful in the Diff panel
2. Every changed file should land in a group. Anything the model leaves out should go into a visible "Other" bucket, so trusting the groups never means missing a file
3. Suggest a reading order: core change first, then where those changes are being put to work, tests, config/infra, and generated files collapsed. The tools I mentioned do this well
4. Reuse the existing Viewed state for per-group progress (e.g. "3/5 viewed")