feat: audit IP/export, webhook replay protection and backend build cleanup

[OladipupuHussein7]

Summary

Audit enrichment, webhook replay protection, and removing the last React/Sentry artifacts from the NestJS backend so it type-checks cleanly.

• GET /admin/audit/actions has no CSV export and the export helper is dead code #1940 Admin audit request metadata — admin action logs capture the caller's IP and User-Agent; migration 1790007000000-AddAdminActionLogRequestMetadata adds the nullable ip / user_agent columns and is reversible.
• Admin audit entries don't capture IP or User-Agent; request-metadata util is unused #1939 Admin audit export — audit records can be exported (with the new request metadata included).
• Payment webhooks have no timestamp tolerance, so a captured valid request can be replayed indefinitely #1938 Webhook replay protection — the sandbox webhook signature is now computed over timestamp + '.' + body, a configurable tolerance (PAYMENT_WEBHOOK_TOLERANCE_SECONDS, default 300s) rejects stale captures, and an event-id ledger in Redis (TTL-scoped, SET NX) acks duplicates without applying them twice; Redis outages fail open so legitimate webhooks aren't dropped.
• React .tsx files live under backend/src/common and don't compile with the backend tsconfig #1937 Frontend/admin component relocation + backend build cleanup — client components (OfflineBanner, AdminBreadcrumbs, AdminToast) are relocated/wired correctly for the app-router layouts, and the backend no longer contains .tsx/React/Sentry references (fixes the pre-existing Cannot find name 'Sentry', missing ./ToastProvider, and randomUUID import errors). npm run build now exits 0 with no TypeScript errors.

Also fixes the duplicate export default AppDataSource that broke migration:run/migration:revert.

Verification

• npm run build → exit 0, zero error TS.
• npx jest src/admin-audit src/payments/payment-webhook.controller.spec.ts src/payments/webhook-replay.service.spec.ts src/payments/adapters/sandbox-rail.adapter.spec.ts → 7 suites / 59 tests passing.
• npm run migration:run and npm run migration:revert verified against a fresh database.

Issues

Closes #1940
Closes #1939
Closes #1938
Closes #1937

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