Add a Vitest setup storage shim for localStorage and sessionStorage when Node/jsdom does not provide usable storage. This fixes the Node 26 frontend CI failures where tests accessed localStorage during setup.
Backend supertest suite for GET /api/security/compare covers tier gating, input validation, cross-node isolation, diff partitioning by vulnerability_id::pkg_name, suppression application, and cross-image comparison. Frontend vitest + React Testing Library scaffolding with component tests for ScanComparisonSheet (loading, error recovery, cross-image warning, filter pills, reload on id change) and SecurityHistoryView (mount fetch, selection cap, oldest-first baseline ordering, tier gating).
Anso