feat: Implement feature graph and JSON document save/load

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

src/Document.cpp

@@ -0,0 +1,90 @@
+#include "Document.h"
+#include "Feature.h"
+#include "SketchFeature.h"
+
+#include <QFile>
+#include <QJsonDocument>
+#include <QJsonArray>
+#include <QJsonObject>
+
+Document::Document(QObject *parent) : QObject(parent)
+{
+}
+
+Document::~Document()
+{
+    clear();
+}
+
+void Document::addFeature(Feature* feature)
+{
+    m_features.append(feature);
+}
+
+void Document::clear()
+{
+    qDeleteAll(m_features);
+    m_features.clear();
+}
+
+bool Document::save(const QString& path) const
+{
+    QJsonArray featuresArray;
+    for (const Feature* feature : m_features) {
+        QJsonObject featureObject;
+        feature->write(featureObject);
+        featuresArray.append(featureObject);
+    }
+
+    QJsonObject rootObject;
+    rootObject["features"] = featuresArray;
+
+    QJsonDocument doc(rootObject);
+    QFile file(path);
+    if (!file.open(QIODevice::WriteOnly)) {
+        return false;
+    }
+
+    file.write(doc.toJson());
+    return true;
+}
+
+bool Document::load(const QString& path)
+{
+    QFile file(path);
+    if (!file.open(QIODevice::ReadOnly)) {
+        return false;
+    }
+
+    QByteArray data = file.readAll();
+    QJsonDocument doc = QJsonDocument::fromJson(data);
+
+    if (doc.isNull() || !doc.isObject()) {
+        return false;
+    }
+
+    clear();
+
+    QJsonObject rootObject = doc.object();
+    if (rootObject.contains("features") && rootObject["features"].isArray()) {
+        QJsonArray featuresArray = rootObject["features"].toArray();
+        for (const QJsonValue& value : featuresArray) {
+            QJsonObject obj = value.toObject();
+            if (obj.contains("type") && obj["type"].isString()) {
+                QString type = obj["type"].toString();
+                Feature* feature = nullptr;
+
+                if (type == "Sketch") {
+                    feature = new SketchFeature("");
+                }
+
+                if (feature) {
+                    feature->read(obj);
+                    addFeature(feature);
+                }
+            }
+        }
+    }
+
+    return true;
+}