Feat/fraud detection system

[shaaibu7]

Implement subscription fraud detection system

Summary

This PR adds a fraud detection workflow for subscription services, covering backend scoring primitives and a mobile fraud operations UI.

What Changed

• Added a new Soroban fraud contract in contracts/fraud
• Implemented multi-signal risk scoring:
  • velocity checks for rapid subscription creation
  • anomalous usage pattern detection
  • chargeback prediction
• Added fraud actions:
  • approve
  • flag
  • block
• Added manual review case support and fraud report generation
• Added shared fraud types to the contract type crate
• Added a persistent fraud store for the React Native app
• Added a dedicated Fraud Dashboard screen
• Wired the Fraud Dashboard into app navigation and Settings

UI / UX

• New fraud dashboard shows:
  • total checks
  • blocked / flagged counts
  • average risk
  • velocity, anomaly, and chargeback alerts
  • manual review queue
  • merchant-level fraud analytics
  • top-risk subscriptions
• Added controls for:
  • approve
  • flag
  • block
  • recalculating fraud signals

Backend Notes

• Added a new contract workspace member for fraud detection
• Fixed the contracts workspace manifest so the new crate compiles cleanly
• Fraud reporting is exposed through:
  • assess_risk(subscriber)
  • flag_subscription(subscription_id)
  • get_fraud_report(merchant_id)

Testing

• cargo test --manifest-path fraud/Cargo.toml --no-run passed
• Added store-level test coverage for fraud queue and review actions

Notes

• jest is not installed in this environment, so the new React Native test could not be executed locally here
• tsc --noEmit is currently blocked by existing repository-wide dependency/type issues outside this feature

closes #194

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[Smartdevs17]

⚠️ Merge conflicts detected

Hi @shaaibu7,

This PR has merge conflicts that must be resolved before it can be merged.

To fix:

1. Sync with the latest main branch: git fetch origin && git merge origin/main
2. Resolve the conflicts in your code
3. Push the resolved changes

Once resolved, the PR will be automatically merged on the next run.

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[shaaibu7]

@Smartdevs17 conflicts resolved