When viewing a commit diff from git history, the GitBranch toggle in the
breadcrumb bar was disabled if the file had no unstaged changes, leaving
no way to return to the editor. Now the toggle stays active whenever
diffMode is true, and a visible "Back to editor" button appears at the
top of the diff view for better discoverability.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>