Feat/36/review lane enforces conventions skill list

[michaelnaughton-euc]

The review lane now gets the .factory/conventions skill list in its rules whenever the file exists in the target checkout, phrased for reviewing: invoke each listed skill and flag every violation as a review comment. lanes/review.md carries the matching instruction, and tests/conventions.sh covers both the injected rules and the missing-file case. Closes #36.

[michaelnaughton-euc]

Thermo-nuclear code quality review of this PR only. Behavior looks correct and the tests cover both the injected-rules and missing-file paths well. No blockers, but there is a code-judo move here that would delete the new branching instead of adding it — details inline. Summary of findings:

1. The review imperative now lives in two homes: lanes/review.md:6 and the header injected by conventions_rules. Implementing lanes keep that imperative in exactly one place (the helper). Pick one home.
2. The new lane mode param on conventions_rules exists only to swap prose. If the imperative sentences move into the lane playbooks, the helper becomes lane-agnostic data emission and the param, the branch, and the duplicated "This repo enables these skills; invoke each one that applies" line all disappear.
3. Minor: run_review in tests copies run_lane's env boilerplate; the RULES+CONVENTIONS assembly is now duplicated verbatim between the feature|bug|docs and review case arms.

Also noting for the record: factory.sh was already over 1000 lines before this PR (1025 → 1035), so this isn't a threshold crossing, but the duplicated rules-assembly in the case arms is the kind of growth that will keep pushing it up.