adversarial-crux-pr

The gate every bashrs lint-rule change passes before a PR is opened. Two halves — an ADVERSARIAL review that tries to break the fix by hunting the false negative it may have introduced, and a CRUX competitive analysis that checks the fix against how shellcheck, mvdan/sh and tree-sitter-bash solve the same problem. Invoke it when the user says "adversarial-crux", "harden this fix", "gate this PR", "crux this lint…