[hugoh]

R in the log picks up the selected commit and reuses the rebase destination picker (onto/after/before) to run jj revert. The destination defaults to the working copy.

Summary

Adds jj revert to gojo: press R on a commit in the log, choose where the reverse should go (onto / after / before a destination), and press ⏎.

Why

gojo had no way to revert a commit. jj revert needs a destination and a placement (--onto / --insert-after / --insert-before), which are the same choices rebase mode already offers, so revert reuses that picker instead of adding a new mode.

Changes

• Runner.Revert runs jj revert -r <src> <placement> <dest>; it supports the same retry-with-extra-flags path as rebase.
• New revert log action bound to R, remappable as log.revert in [keymap].
• Rebase mode gets a revert variant: the status bar shows [revert], the source is marked "● reverting", and the -r/-s scope toggle is disabled.
• The destination starts on the working copy if it's in the log (it can be the reverted commit itself); otherwise it falls back to the neighboring commit, like rebase. Revert allows destination = source; rebase still rejects it.
• execRebase now has one run path shared by rebase and revert.
• R / revert appears in the help view, the log right-click menu and the shortcut bar.
• CHANGELOG: entry under Unreleased → Added.

Checklist

• go build ./... passes
• go vet ./... passes
• go test ./... passes
• Tests added/updated for behavior changes (TestRevertModeFlow, TestRevertDefaultDestination, keymap resolution)
• Docs updated (README / AGENTS.md / CONTRIBUTING.md) if relevant