Adds workflow.code_review_command config key that allows solo devs to
plug external AI review tools into the ship flow. When configured, the
ship workflow generates a diff, builds a review prompt with stats and
phase context, pipes it to the command via stdin, and parses JSON output
with verdict/confidence/issues. Handles timeout (120s) and failures
gracefully by falling through to the existing manual review flow.
Closes#1876
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
