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/css/style.css

@@ -0,0 +1,63 @@
+/* Basic Reset and Typography */
+body {
+    font-family: Arial, sans-serif;
+    margin: 0;
+    padding: 0;
+    line-height: 1.6;
+    background-color: #f4f4f4;
+    color: #333;
+}
+
+header {
+    background-color: #333;
+    color: #fff;
+    padding: 20px 0;
+    text-align: center;
+}
+
+header h1 {
+    margin: 0;
+}
+
+nav ul {
+    list-style: none;
+    padding: 0;
+}
+
+nav ul li {
+    display: inline;
+    margin: 0 15px;
+}
+
+nav ul li a {
+    color: #fff;
+    text-decoration: none;
+}
+
+nav ul li a:hover {
+    text-decoration: underline;
+}
+
+main {
+    padding: 20px;
+    max-width: 1200px;
+    margin: auto;
+}
+
+footer {
+    background-color: #333;
+    color: #fff;
+    text-align: center;
+    padding: 10px 0;
+    position: fixed;
+    width: 100%;
+    bottom: 0;
+}
+
+/* Responsive Design */
+@media (max-width: 768px) {
+    nav ul li {
+        display: block;
+        margin: 10px 0;
+    }
+}