feat: Add unit tests, structured logging, health checks, and response validation

[alperenkocyigit]

This commit implements four major features to improve code quality, developer experience, and production readiness:

1. Unit Testing Framework (Vitest)

   • Add comprehensive test suite for token-manager package
   • Add tests for payload-helper utilities
   • Add tests for mcp-client core functionality
   • Configure Vitest with coverage reporting
   • Add test scripts: test, test:watch, test:coverage

2. Structured Logging (Pino)

   • Implement structured JSON logging with Pino
   • Create logger utility with configurable log levels
   • Replace console.log with structured logger in core code
   • Add pino-pretty for development-friendly output
   • Support LOG_LEVEL environment variable

3. Health Check Utility

   • Add healthCheck() method to VisaMcpClient
   • Check connection status, server reachability, and token validity
   • Return detailed health status with available tools count
   • Integrate with structured logging

4. Response Validation (Zod)

   • Create Zod schemas for all MCP tool responses
   • Implement automatic response validation in callTool()
   • Add validateResponses config option (default: true)
   • Provide detailed validation error messages
   • Support optional validation for flexibility

Files changed:

• Add CHANGELOG.md with detailed documentation
• Add vitest.config.ts for both packages
• Add test files: *.test.ts
• Add src/utils/logger.ts
• Add src/schemas/tool-responses.ts
• Update package.json files with new dependencies
• Update mcp-client.ts with validation and health checks
• Update workflow-helpers.ts with structured logging

Dependencies added:

• pino@^9.6.0, pino-pretty@^13.0.0
• vitest@^2.1.8, @vitest/coverage-v8@^2.1.8

All changes are backwards compatible and fully documented.