docs: update resources API docs

docs/api/resources/shader/getsourcecode.md

@@ -0,0 +1,24 @@
+# Shader::GetSourceCode
+
+```cpp
+const Containers::String& GetSourceCode() const
+```
+
+获取着色器源码。
+
+**返回：** `const Containers::String&` - 着色器源码的引用
+
+**线程安全：** ❌ 非线程安全
+
+**复杂度：** O(1)
+
+**示例：**
+
+```cpp
+ResourceHandle<Shader> shader = ResourceManager::Get().Load<Shader>("shaders/vertex.glsl");
+const Containers::String& source = shader->GetSourceCode();
+```
+
+## 相关文档
+
+- [Shader 总览](shader.md) - 返回类总览