SQL diagnostics for purchase_trade business rules

These scripts are read-only diagnostics for a PostgreSQL test database.

quantity_consistency_checks.sql

Checks the two core lot quantity invariants documented in lots-and-quantities.md and lots-and-quantities.en.md.

Run it on a restored test database:

\i modules/purchase_trade/docs/business/sql/quantity_consistency_checks.sql

The script returns rows only when it finds a potential issue.

Main columns:

check_name: invariant or diagnostic that failed.
line_id: purchase.line or sale.line id depending on the check.
virtual_lot_id: virtual lot involved in the inconsistency.
observed_value: value found in the database.
expected_value: value required by the business rule.
diff: observed minus expected.
detail: human-readable explanation.

Cross-category UoM rows are reported as manual-review diagnostics because the Python code may pass explicit conversion factors that cannot be inferred safely from SQL alone.