feat(check-product): rule-10 layout gate + auto-merge permissions fix (P3.6 B7) (#19)

* feat(check-product): rule-10 bans grab-bag filenames and multi-constructor files

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(ci): grant auto-merge job contents:write (enablePullRequestAutoMerge requirement)

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>