feat(security-posture): implement Security Posture Scoring System (#153)

[iyanumajekodunmi756]

Summary

Implements the Security Posture Scoring System as specified in issue #153.

Changes

New module: src/modules/security-posture/

File	Description
interfaces/security-posture.interface.ts	ScoringFactor, PostureSnapshot, SecurityPostureResult types
security-posture.service.ts	Weighted scoring engine, history tracking, grade + trend logic
security-posture.controller.ts	GET /security-posture and GET /security-posture/history endpoints
security-posture.module.ts	NestJS module declaration
security-posture.service.spec.ts	13 unit tests

Modified

• apps/backend/src/app.module.ts — registers SecurityPostureModule

Acceptance Criteria

• Scores calculated — SecurityPostureService.getPosture() computes a weighted 0–100 score from 5 factors
• Trends available — trend field returns improving | stable | degrading based on last two snapshots; GET /security-posture/history returns full history
• Results displayed — GET /security-posture returns score, grade (A–F), weighted factors, history, and trend

Scoring Model

Five weighted factors (weights sum to 1.0):

Factor	Weight
unresolvedCriticalAlerts	35%
mempoolThreatDensity	25%
watchlistCoverage	20%
notificationReliability	10%
auditLogCompleteness	10%

History is capped at 30 snapshots, seeded with 7 days of synthetic data on first boot.

Tests

PASS apps/backend/src/modules/security-posture/security-posture.service.spec.ts
  SecurityPostureService
    ✓ should be defined
    getPosture
      ✓ returns a score between 0 and 100
      ✓ returns a valid grade
      ✓ returns a valid ISO timestamp in calculatedAt
      ✓ returns factors with weights that sum to 1.0
      ✓ each factor has a valid weighted score equal to value * weight
      ✓ returns a non-empty history array
      ✓ returns a valid trend value
      ✓ grade A corresponds to score >= 90
      ✓ history length does not exceed 30 snapshots
    getHistory
      ✓ returns an array of snapshots
      ✓ each snapshot has a numeric score and ISO timestamp
      ✓ returns a copy — mutations do not affect internal state

Tests: 13 passed, 13 total

Full backend suite: 22/22 passed. Lint and format checks: clean.

Closes #153

[mijinummi]

Hi @iyanumajekodunmi756 , thanks for your contributions, please kindly fix the remaining ci failures, please due ensure the all ci passed successfully. Well done for this effort you have put in so far.

[mijinummi]

Hi @iyanumajekodunmi756 thank you for fixing some of the errors, please resolve conflict, pull from main and update your branch, fix typescript error and commit again. Well done