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.

packages/nebula-ui/qml/Nebula/UI/NebulaIcon.qml

@@ -82,6 +82,18 @@ Item {
         case "application":
             paintApplication(ctx)
             break
+        case "minimize":
+            paintMinimize(ctx)
+            break
+        case "maximize":
+            paintMaximize(ctx)
+            break
+        case "restore":
+            paintRestore(ctx)
+            break
+        case "close":
+            paintClose(ctx)
+            break
         default:
             paintApplication(ctx)
             break
@@ -192,6 +204,41 @@ Item {
         ctx.stroke()
     }
 
+    function paintMinimize(ctx) {
+        ctx.lineWidth = 1.7
+        ctx.beginPath()
+        ctx.moveTo(6.4, 16.2)
+        ctx.lineTo(17.6, 16.2)
+        ctx.stroke()
+    }
+
+    function paintMaximize(ctx) {
+        ctx.lineWidth = 1.5
+        ctx.beginPath()
+        roundedRect(ctx, 6.2, 6.2, 11.6, 11.6, 2)
+        ctx.stroke()
+    }
+
+    function paintRestore(ctx) {
+        ctx.lineWidth = 1.45
+        ctx.beginPath()
+        roundedRect(ctx, 8.6, 5.6, 9.4, 9.4, 1.7)
+        ctx.stroke()
+        ctx.beginPath()
+        roundedRect(ctx, 5.6, 8.6, 9.4, 9.4, 1.7)
+        ctx.stroke()
+    }
+
+    function paintClose(ctx) {
+        ctx.lineWidth = 1.7
+        ctx.beginPath()
+        ctx.moveTo(7.3, 7.3)
+        ctx.lineTo(16.7, 16.7)
+        ctx.moveTo(16.7, 7.3)
+        ctx.lineTo(7.3, 16.7)
+        ctx.stroke()
+    }
+
     function paintApplication(ctx) {
         ctx.lineWidth = 1.5
         ctx.beginPath()