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.

shells/desktop/shell/qml/components/Launcher.qml

@@ -1,6 +1,7 @@
 import QtQuick
 import Nebula.UI
 import Nebula.Applications
+import Nebula.Windows
 
 Item {
     id: root
@@ -187,6 +188,33 @@ Item {
                     }
                 }
 
+                Column {
+                    width: parent.width
+                    spacing: 8
+                    visible: !root.searching && WindowService.windowCount > 0
+
+                    Text {
+                        text: qsTr("Open Windows")
+                        color: Theme.textSecondary
+                        font.family: Theme.fontFamily
+                        font.pixelSize: Theme.fontSizeSmall
+                        font.weight: Font.DemiBold
+                        font.letterSpacing: 0.4
+                    }
+
+                    Column {
+                        width: parent.width
+                        spacing: 2
+
+                        Repeater {
+                            model: WindowService.model
+                            delegate: OpenWindowItem {
+                                width: parent.width
+                            }
+                        }
+                    }
+                }
+
                 Column {
                     width: parent.width
                     spacing: 8