Add Nebula.Windows with Sway IPC backend

Introduces a new `core/windows` module (`Nebula.Windows`) with `WindowService`, window/workspace models, and a Sway IPC backend for live window tracking and control (focus, close, move/resize, snap, maximize/restore, minimize, workspace switch). The desktop shell now links this module, uses compositor focus for top-bar active app text, and adds an Open Windows section in the launcher with focus/close actions.

Also updates application metadata handling to parse `StartupWMClass` and map window `app_id`/class to friendly names and icons, and revises Sway config/docs for the new floating-first Desktop 0.2 behavior with temporary compositor-provided decorations.

core/windows/WindowModel.hpp

@@ -0,0 +1,54 @@
+#pragma once
+
+#include "WindowTypes.hpp"
+
+#include <QAbstractListModel>
+#include <QVector>
+#include <QtQml/qqmlregistration.h>
+
+class WindowModel : public QAbstractListModel
+{
+    Q_OBJECT
+    QML_ELEMENT
+    QML_UNCREATABLE("Obtained from WindowService")
+    Q_PROPERTY(int count READ count NOTIFY countChanged)
+
+public:
+    enum Roles {
+        WindowIdRole = Qt::UserRole + 1,
+        TitleRole,
+        AppIdRole,
+        WindowClassRole,
+        WorkspaceRole,
+        FocusedRole,
+        FloatingRole,
+        FullscreenRole,
+        XRole,
+        YRole,
+        WidthRole,
+        HeightRole,
+        DisplayNameRole,
+        IconNameRole,
+        MinimizedRole,
+        MaximizedRole,
+        OutputRole
+    };
+    Q_ENUM(Roles)
+
+    explicit WindowModel(QObject *parent = nullptr);
+
+    int rowCount(const QModelIndex &parent = QModelIndex()) const override;
+    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
+    QHash<int, QByteArray> roleNames() const override;
+
+    int count() const;
+    void setWindows(QVector<WindowInfo> windows);
+    const WindowInfo *windowAt(int row) const;
+    const WindowInfo *windowById(qint64 windowId) const;
+
+signals:
+    void countChanged();
+
+private:
+    QVector<WindowInfo> m_windows;
+};