feat(soroban): add contract risk analyzer module (#149)

[A6dulmalik]

• add RiskAnalyzerService with pattern matching against soroban.json signatures
• add RiskAnalyzerController exposing POST /soroban/risk/analyze
• add RiskAnalyzerModule registered in AppModule
• add 8 unit tests covering all risk scoring scenarios

Description

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Related Issues

Closes #149

Changes Made

Testing

• I have tested these changes locally
• Tests pass locally (npm run test)
• Linting passes (npm run lint)
• Code is formatted (npm run format)
• TypeScript builds successfully (npm run build)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings or errors
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests passed with my changes

Screenshots (if applicable)

Additional Context

[mijinummi]

LGTM!