Backport columnar-independent scope fixes

[platypii]

Summary

• preserve table and outer-row scope across scans, private batches, aggregates, CTEs, and set operations
• request struct base columns for projection and ordering
• prevent unresolved projections from advertising incomplete materialized rows
• add nine regressions using APIs already supported by master

Prepared-scan contracts, demand scheduling, caching, and residual execution remain scoped to columnar-design.

Validation

• npm test: 1,945 passed
• npm run lint
• npx tsc