feat: introduce v2.0 abstraction layer with core types, backend interface, and plugin system

feat: add fade effects with API control and real-time event subscription
test: add API integration tests with isolated test environment and coverage reporting
build: update Makefile for recursive source finding, dynamic linking, and test targets
docs: document abstraction layer, fade effects, and API enhancements in README

tests/project_root/js/main.js

@@ -0,0 +1,9 @@
+// Main JavaScript file for future enhancements
+
+// Example: Smooth scroll for navigation links
+document.querySelectorAll('nav a').forEach(link => {
+    link.addEventListener('click', function(e) {
+        e.preventDefault();
+        document.querySelector(this.getAttribute('href')).scrollIntoView({ behavior: 'smooth' });
+    });
+});