`SEVERITY_ORDER` drifts across the codebase

The SEVERITY_ORDER map is duplicated across 5 different files and the copies have drifted in two different ways.

1. in 2 places (enrich, export) the rank of MEDIUM and HIGH_BUG are swapped compared to others.
2. sandbox/partitioner.ts is missing LOW for the --min-severity filter which is its own bug, meaning any --min-severity threshold above LOW still includes LOW findings.

The Severity type itself lists CRITICAL | HIGH | MEDIUM | HIGH_BUG | BUG | LOW which I assume is the intended order.