Finding UUID Migration Phase 3: Add NOT NULL constraint to new_uuid

Problem

After Phase 2 backfills new_uuid for all existing findings, we need to add a NOT NULL constraint to ensure data integrity going forward.

Implementation

1. Verify BBM from Phase 2 has completed and no NULL values remain
2. Add NOT NULL constraint to new_uuid column on vulnerability_occurrences table
3. Use appropriate migration strategy for large tables (async constraint validation)

Acceptance Criteria

• Verified no NULL values exist in new_uuid column
• NOT NULL constraint added successfully
• No downtime or performance impact

Dependencies

• Blocked by Phase 2 (backfill must complete first)

Related

• Part of Finding UUID migration series
• #587625 (closed) - Phase 1: Start populating new_uuid