docs(review): add quality gates map

[stacknil]

Summary

• add docs/quality-gates.md as a reviewer evidence map across LGL-01 through LGL-06 surfaces
• map parser conformance, parser coverage, report snapshots, rule explainability, false-positive boundaries, parser failure taxonomy, performance envelope, and public safety boundaries to concrete tests/fixtures/docs
• link the quality gates map from README, reviewer path, and reviewer brief

Validation

• ctest --test-dir build -C Release --output-on-failure
• git diff --check
• git diff --cached --check
• privacy/secret scan on changed docs