Consolidate fraud heuristics into a scored rules engine

## Background
Fraud checks are scattered boolean heuristics that are hard to tune. Consolidate them into a single scored engine.

## Files to modify (2-3)
src/hooks/useFraudDetection.ts
src/services/bundleSecurityContext.ts

## Acceptance Criteria

Implemented across the listed files

Unit/integration tests added or updated and passing

No regression; follows project coding standards
