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.cpp

@@ -0,0 +1,114 @@
+#include "WindowModel.hpp"
+
+#include <utility>
+
+WindowModel::WindowModel(QObject *parent)
+    : QAbstractListModel(parent)
+{
+}
+
+int WindowModel::rowCount(const QModelIndex &parent) const
+{
+    if (parent.isValid())
+        return 0;
+    return m_windows.size();
+}
+
+int WindowModel::count() const
+{
+    return m_windows.size();
+}
+
+QVariant WindowModel::data(const QModelIndex &index, int role) const
+{
+    if (!index.isValid() || index.row() < 0 || index.row() >= m_windows.size())
+        return {};
+
+    const WindowInfo &window = m_windows.at(index.row());
+    switch (role) {
+    case WindowIdRole:
+        return QString::number(window.id);
+    case TitleRole:
+        return window.title;
+    case AppIdRole:
+        return window.appId;
+    case WindowClassRole:
+        return window.windowClass;
+    case WorkspaceRole:
+        return window.workspace;
+    case FocusedRole:
+        return window.focused;
+    case FloatingRole:
+        return window.floating;
+    case FullscreenRole:
+        return window.fullscreen;
+    case XRole:
+        return window.x;
+    case YRole:
+        return window.y;
+    case WidthRole:
+        return window.width;
+    case HeightRole:
+        return window.height;
+    case DisplayNameRole:
+    case Qt::DisplayRole:
+        return window.displayName.isEmpty() ? window.title : window.displayName;
+    case IconNameRole:
+        return window.iconName;
+    case MinimizedRole:
+        return window.minimized;
+    case MaximizedRole:
+        return window.maximized;
+    case OutputRole:
+        return window.output;
+    default:
+        return {};
+    }
+}
+
+QHash<int, QByteArray> WindowModel::roleNames() const
+{
+    return {
+        {WindowIdRole, QByteArrayLiteral("windowId")},
+        {TitleRole, QByteArrayLiteral("title")},
+        {AppIdRole, QByteArrayLiteral("appId")},
+        {WindowClassRole, QByteArrayLiteral("windowClass")},
+        {WorkspaceRole, QByteArrayLiteral("workspace")},
+        {FocusedRole, QByteArrayLiteral("focused")},
+        {FloatingRole, QByteArrayLiteral("floating")},
+        {FullscreenRole, QByteArrayLiteral("fullscreen")},
+        {XRole, QByteArrayLiteral("x")},
+        {YRole, QByteArrayLiteral("y")},
+        {WidthRole, QByteArrayLiteral("width")},
+        {HeightRole, QByteArrayLiteral("height")},
+        {DisplayNameRole, QByteArrayLiteral("displayName")},
+        {IconNameRole, QByteArrayLiteral("iconName")},
+        {MinimizedRole, QByteArrayLiteral("minimized")},
+        {MaximizedRole, QByteArrayLiteral("maximized")},
+        {OutputRole, QByteArrayLiteral("output")},
+    };
+}
+
+void WindowModel::setWindows(QVector<WindowInfo> windows)
+{
+    beginResetModel();
+    m_windows = std::move(windows);
+    endResetModel();
+    emit countChanged();
+}
+
+const WindowInfo *WindowModel::windowAt(int row) const
+{
+    if (row < 0 || row >= m_windows.size())
+        return nullptr;
+    return &m_windows.at(row);
+}
+
+const WindowInfo *WindowModel::windowById(qint64 windowId) const
+{
+    for (const WindowInfo &window : m_windows) {
+        if (window.id == windowId)
+            return &window;
+    }
+    return nullptr;
+}