feat: implement consistent risk scoring engine for invoices

[EDOHWARES]

Description

Implemented the RiskService to replace our placeholder logic. It now calculates a consistent invoice risk score (0-100) based on the invoice amount and date.

Key Changes

• New Service: Created RiskService alongside a calculateScore(amount, date) method.
• Scoring Rules:
  • amount > $10,000 starts at a base score of 80.
  • amount < $1,000 starts at a base score of 95.
  • All other amounts start at a base score of 90.
• Deterministic AI Simulation: Implemented a hashing algorithm that generates a consistent pseudo-random variance (-5 to +5) based on the input payload.
• Edge-case safety: Enforced strict bounds ensuring the final score never exceeds 100 or drops below 0.
• Testing: Added Jest coverage validating all Acceptance Criteria.

Acceptance Criteria Covered

• Inputting the same invoice data returns a consistent score.
• Score is always a strict integer between 0 and 100.
• Slight variance applied to simulate AI analysis.

Closes #5

[AlAfiz]

@EDOHWARES resolve conflicts

[Nathydre]

@EDOHWARES ,good day,you pull request has a conflict,please do checkup on it and fix so i can merge, thank you