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/WorkspaceModel.cpp

@@ -0,0 +1,84 @@
+#include "WorkspaceModel.hpp"
+
+#include <utility>
+
+WorkspaceModel::WorkspaceModel(QObject *parent)
+    : QAbstractListModel(parent)
+{
+}
+
+int WorkspaceModel::rowCount(const QModelIndex &parent) const
+{
+    if (parent.isValid())
+        return 0;
+    return m_workspaces.size();
+}
+
+int WorkspaceModel::count() const
+{
+    return m_workspaces.size();
+}
+
+QVariant WorkspaceModel::data(const QModelIndex &index, int role) const
+{
+    if (!index.isValid() || index.row() < 0 || index.row() >= m_workspaces.size())
+        return {};
+
+    const WorkspaceInfo &workspace = m_workspaces.at(index.row());
+    switch (role) {
+    case WorkspaceIdRole:
+        return workspace.id;
+    case NameRole:
+    case Qt::DisplayRole:
+        return workspace.name;
+    case NumberRole:
+        return workspace.number;
+    case FocusedRole:
+        return workspace.focused;
+    case VisibleRole:
+        return workspace.visible;
+    case OutputRole:
+        return workspace.output;
+    case WindowCountRole:
+        return workspace.windowCount;
+    default:
+        return {};
+    }
+}
+
+QHash<int, QByteArray> WorkspaceModel::roleNames() const
+{
+    return {
+        {WorkspaceIdRole, QByteArrayLiteral("workspaceId")},
+        {NameRole, QByteArrayLiteral("name")},
+        {NumberRole, QByteArrayLiteral("number")},
+        {FocusedRole, QByteArrayLiteral("focused")},
+        {VisibleRole, QByteArrayLiteral("visible")},
+        {OutputRole, QByteArrayLiteral("output")},
+        {WindowCountRole, QByteArrayLiteral("windowCount")},
+    };
+}
+
+void WorkspaceModel::setWorkspaces(QVector<WorkspaceInfo> workspaces)
+{
+    beginResetModel();
+    m_workspaces = std::move(workspaces);
+    endResetModel();
+    emit countChanged();
+}
+
+const WorkspaceInfo *WorkspaceModel::workspaceAt(int row) const
+{
+    if (row < 0 || row >= m_workspaces.size())
+        return nullptr;
+    return &m_workspaces.at(row);
+}
+
+const WorkspaceInfo *WorkspaceModel::focusedWorkspace() const
+{
+    for (const WorkspaceInfo &workspace : m_workspaces) {
+        if (workspace.focused)
+            return &workspace;
+    }
+    return nullptr;
+}