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/DesktopEntry.cpp

@@ -353,6 +353,8 @@ DesktopEntry parseDesktopEntryFile(const QString &filePath, const QString &deskt
             entry.exec = value;
         else if (key == QLatin1String("TryExec"))
             entry.tryExec = value;
+        else if (key == QLatin1String("StartupWMClass"))
+            entry.startupWmClass = value;
         else if (key == QLatin1String("Icon"))
             entry.icon = value;
         else if (key == QLatin1String("Path"))