Add portfolio screenshot standard and completed project captures

[mizcausevic-dev]

Summary

• adds a reusable screenshot standard for portfolio repositories
• adds completed screenshot assets for this project
• embeds the screenshots directly into the README

Details

• documents naming, sizing, and placement standards for screenshots across frontend, backend, and data projects
• adds a screenshots/ folder convention for future repository work
• captures a live Swagger UI overview for the running API
• adds a polished lead scoring workflow visual based on the live score response
• adds a validation proof visual based on the passing API test run

Validation

• npm test
• local screenshot capture from the running API and generated proof pages