Fix stale and mismatched course hyperlinks in README.md

[Copilot]

Several course links in README.md pointed to the wrong course, a deprecated path, or a decommissioned provider portal. Four links corrected:

• Version Control with Git (Atlassian): URL was resolving to Google's "Introduction to Git and GitHub" — fixed to coursera.org/learn/version-control-with-git
• Network Security & Database Vulnerabilities (RIT/edX): slug network-security belongs to a different institution — fixed to edx.org/course/network-security-2
• Cybersecurity Basics (IBM): ibm.com/training/course/cybersecurity-basics portal decommissioned — updated to coursera.org/learn/ibm-cyber-security
• Android app development (Google): "Android Basics in Kotlin" pathway deprecated — updated title to "Android Basics with Compose" and URL to developer.android.com/courses/android-basics-compose/course

All remaining 30+ links verified correct; no structural or content changes beyond the four link corrections.