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

manual/building.html

@@ -13,7 +13,7 @@
         <aside class="sidebar">
             <div class="sidebar-header">
                 <h1>DWN</h1>
-                <span class="version">v1.0.0</span>
+                <span class="version">v2.0.0</span>
             </div>
 
             <div class="search-box">
@@ -47,6 +47,8 @@
                 <div class="nav-section">
                     <div class="nav-section-title">Advanced</div>
                     <a href="architecture.html" class="nav-link">Architecture</a>
+                    <a href="abstraction-layer.html" class="nav-link">Abstraction Layer</a>
+                    <a href="plugin-development.html" class="nav-link">Plugin Development</a>
                     <a href="building.html" class="nav-link active">Building from Source</a>
                 </div>
             </nav>