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/applications/ApplicationModel.hpp

@@ -35,6 +35,7 @@ public:
     void setEntries(QVector<DesktopEntry> entries);
     const DesktopEntry *entryAt(int row) const;
     const DesktopEntry *entryById(const QString &desktopId) const;
+    const DesktopEntry *entryMatchingWindow(const QString &appId, const QString &windowClass) const;
 
 signals:
     void countChanged();