feat: Implement feature graph and JSON document save/load

Co-authored-by: aider (gemini/gemini-2.5-pro) <aider@aider.chat>

src/Feature.cpp

@@ -0,0 +1,28 @@
+#include "Feature.h"
+
+Feature::Feature(const QString& name) : m_name(name)
+{
+}
+
+QString Feature::name() const
+{
+    return m_name;
+}
+
+void Feature::setName(const QString& name)
+{
+    m_name = name;
+}
+
+void Feature::read(const QJsonObject& json)
+{
+    if (json.contains("name") && json["name"].isString()) {
+        m_name = json["name"].toString();
+    }
+}
+
+void Feature::write(QJsonObject& json) const
+{
+    json["type"] = type();
+    json["name"] = m_name;
+}