docs: add 14-article Software Engineering Principles series Full series covering: Introduction to SE, SDLC, OOP, SOLID Principles, Design Patterns (GoF), Clean Code, Software Architecture, Refactoring, Testing Principles, Version Control & Git Workflows, API Design, Security Principles (OWASP Top 10), Database Design, Agile & Scrum. Each article includes detailed explanations, Java code examples, and forward/back navigation. Index updated with reading paths by task. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

buddhika75 committed Jun 8, 2026