[Enhancement] No claim submission fraud detection

[nonsobethel0-dev]

No fraud detection for claim submissions. Duplicate or fraudulent claims not caught.

Files: contracts/claims-processor/src/lib.rs

Fix: Add fraud detection rules and scoring.

[Bobai100]

@Bobai100 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi Maintainer,
I’d really appreciate the opportunity to work on this issue. Having reviewed the acceptance criteria, I’m confident that I can submit a PR after being assigned.
Please kindly assign this issue to me.
Thank you!

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[clintjeff2]

@clintjeff2 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hello, I have 6 years of experience working on tasks like this and handling similar challenges across backend, frontend, and smart-contract development. I have carefully read and fully understood the task requirements, and I am confident I can deliver a clean, efficient, and well-tested solution promptly. I always ensure high-quality implementation, maintainability, and adherence to best practices.

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[Labi-Joy]

@Labi-Joy has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hi, I would like to pick this up.

Approach

• Claim fingerprint: hash of policy id + incident id + claimant + normalized amount + timestamp bucket, stored on submission. Exact match rejects with DuplicateClaim.
• Fraud score (0 to 100) from weighted rules: same claimant + policy within cooldown, amount above cap, rapid resubmission after denial, partial fingerprint collision.
• Below soft_threshold: accept. Between soft and hard_threshold: accept with FraudReview event. At or above hard: reject with SuspectedFraud.Thresholds admin-settable, defaults conservative. Weights in one const block.
  Tests
• Exact duplicate rejected.
• Resubmission after denial flagged.
• Amount above cap flagged.
• Clean claim passes.
• Admin-only threshold updates.
  PR
• Branch feat/claim-fraud-detection, PR body lists rules, weights, defaults.

Estimate: ~1 day.

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