Fix Linux popup z-order inset drift (CSD title bar)

The custom CSD title bar is drawn inside the same Compose scene as the
content (not as external inset), so platform inset reporting distorts popup
positioning. Setting topInsetPx=0 prevents Compose's RootMeasurePolicy from
shifting popups downward. Popups naturally layer above the title bar via
ComposeSceneLayer z-order.

Author: kdroidFilter

decorated-window-tao/src/main/kotlin/dev/nucleusframework/window/tao/render/TaoComposeSceneHostLinux.kt

@@ -278,7 +278,23 @@ internal class TaoComposeSceneHostLinux(
                 platformContext =
                     LinuxTaoPlatformContext(
                         windowHandle = window.handle,
-                        topInsetPx = { (titleBarHeightDpState.value * scale).toInt() },
+                        // The custom CSD title bar is drawn inside the same Compose
+                        // scene as the rest of the content, so it shares the (0, 0)
+                        // origin with everything else. We must NOT report it as a
+                        // `PlatformInsets.top`: Compose's `RootMeasurePolicy` (cf.
+                        // `RootMeasurePolicy.skiko.kt::positionWithInsets`) applies
+                        // platform insets as an *additive offset* on the popup
+                        // position (designed for iOS notches / Android status
+                        // bars, where the safe area is outside the Compose surface).
+                        // Reporting `top = titleBarHeight` here shifts every Popup,
+                        // DropdownMenu, ContextMenu, and Tooltip down by that
+                        // amount — visible as a consistent "title-bar-height
+                        // downward drift" of every popup the user opens. Popups
+                        // are free to overlap the title bar zone; the title bar
+                        // composable's own z-order keeps it visually on top of
+                        // the page content but popups (rendered in a higher
+                        // ComposeSceneLayer) naturally float above both.
+                        topInsetPx = { 0 },
                         windowInfo = windowInfo,
                         semanticsOwnerListener = semanticsOwnerListener,
                         dragAndDropManager = dndManager,