Add focused window controls to top bar

Introduces a new `WindowControls` component in the desktop top bar with minimize, maximize/restore, and close actions for the focused window. `WindowService` now exposes focused-window presence/maximized state plus focused-window convenience actions to support this UI.

Also extends Nebula UI with a reusable `NebulaToolTip`, keyboard/pressed-state support in `NebulaIconButton`, new window-control glyphs in `NebulaIcon`, and theme tokens for pressed/danger hover states, with CMake and README updates to register/document the new components.

shells/desktop/shell/qml/components/TopBar.qml

@@ -23,15 +23,19 @@ Item {
         id: left
         anchors.left: parent.left
         anchors.leftMargin: 6
+        anchors.right: right.left
+        anchors.rightMargin: 12
         anchors.verticalCenter: parent.verticalCenter
         spacing: 8
 
         NebulaButton {
+            id: nebulaButton
             checked: ShellState.launcherOpen
             onClicked: ShellState.toggleLauncher()
         }
 
         Rectangle {
+            id: leftDivider
             anchors.verticalCenter: parent.verticalCenter
             width: 1
             height: 14
@@ -40,7 +44,7 @@ Item {
 
         Text {
             anchors.verticalCenter: parent.verticalCenter
-            width: Math.min(implicitWidth, root.width * 0.4)
+            width: Math.min(implicitWidth, Math.max(0, left.width - nebulaButton.width - leftDivider.width - left.spacing * 2))
             text: ShellState.activeApplication
             color: Theme.textSecondary
             font.family: Theme.fontFamily
@@ -50,9 +54,28 @@ Item {
         }
     }
 
-    SystemArea {
+    Row {
+        id: right
         anchors.right: parent.right
         anchors.rightMargin: 10
         anchors.verticalCenter: parent.verticalCenter
+        spacing: windowControls.visible ? 8 : 0
+
+        WindowControls {
+            id: windowControls
+            anchors.verticalCenter: parent.verticalCenter
+        }
+
+        Rectangle {
+            visible: windowControls.visible
+            width: visible ? 1 : 0
+            height: 14
+            color: Theme.borderStrong
+            anchors.verticalCenter: parent.verticalCenter
+        }
+
+        SystemArea {
+            anchors.verticalCenter: parent.verticalCenter
+        }
     }
 }