Fix v1.7.4 analyzer false positives

[alxxjohn]

Summary

• ignore nested Go function literal returns in return-contract scans
• treat repository command bool/error methods as explicit mutation boundaries
• demote maintainability history findings to advisory artifacts by default
• narrow boolean predicate naming to strong boolean value evidence

Verification

• go test ./...
• make fmt-check
• make table-diff BASE_REF=main (Code Quality passed)
• make table (Code Quality passed; command still exits nonzero due unrelated CI/CD failure and govulncheck warning)