Superadmin impersonation, hardened auth/upload paths, dependency updates
- Add superadmin impersonation: sessions.impersonated_by (migration 0003) is
stamped onto audit rows so impersonated actions are attributable, with a
persistent ImpersonationBanner in the app shell.
- Harden auth and upload handling across routes (safe redirect targets,
filename sanitization, checkout grant handling).
- Update dependencies: Sentry 8 -> 10, @fastify/static 8 -> 10,
react-router-dom 6.30.6; add find-my-way / fast-uri overrides.
- Add tests for safe-next, checkout-grant, and upload-filename.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
