feat(application): parent FileKit dialogs to a Nucleus window

[kdroidFilter]

Summary

• Adds NucleusWindow.withFileKitDialogSettings { settings -> … } to nucleus-application: it runs the block with FileKitDialogSettings.parent set from the window's platform identity, so FileKit pickers attach to the window instead of floating free.
• filekit-dialogs is compileOnly (like filekit-core): never forced on consumers, only callable by an app that already ships it.
• Bumps FileKit to 0.16.0 (no dialog-parent changes vs 0.15: FileKitDialogParent, FileKitDialogSettings and MacOSFilePicker are identical).
• Why not fully automatic: FileKit (0.15 and 0.16) has no global parent hook (FileKitDialogSettings.createDefault() always returns parent = null), and reflection / patching FileKit's bytecode are off the table. A follow-up upstream PR adding a parent provider to FileKit would let nucleusApplication register it and make a bare FileKit.openFilePicker() parented.

Documentation

Attach a FileKit dialog to a window

Wrap the FileKit call in withFileKitDialogSettings on the window that opens it:

val window = LocalNucleusWindow.current
val scope = rememberCoroutineScope()

Button(onClick = {
    scope.launch {
        val file = window.withFileKitDialogSettings { settings ->
            FileKit.openFilePicker(dialogSettings = settings)
        }
    }
}) { Text("Open…") }

Pass your own settings as the first argument to keep a title or macOS options; only parent is filled in:

window.withFileKitDialogSettings(FileKitDialogSettings(title = "Import")) { settings ->
    FileKit.openFileSaver(suggestedName = "export", extension = "csv", dialogSettings = settings)
}

Platform	Parent
Windows	the window's HWND (FileKitDialogParent.windows)
Linux X11 / XWayland	x11:<xid> (FileKitDialogParent.x11)
Linux Wayland	an xdg_foreign export (FileKitDialogParent.wayland), opened before the block and closed when it returns or throws
macOS	none — not needed: FileKit's NSOpenPanel / NSSavePanel.runModal() runs NSApplication.runModal(for:), which is app-modal (no other window takes events while it is up). A parent would only turn it into a sheet, a presentation choice

Behaviour:

• Settings that already carry a parent are passed through untouched.
• When the window exposes no platform identity (not realized yet, native bridge missing) the settings are passed through unparented.
• The Wayland export waits for the compositor, so the parent is resolved on Dispatchers.IO; calling from the UI thread is fine.
• The manual path (nucleusWindow.unsafe.taoWindow?.nativeHandle / xdgPortalParent()) still works for other portal dialogs.

Test plan

• FileKitDialogsTest: parent applied and lease released after the dialog, lease released when the picker throws, caller-chosen parent kept, no identity → unparented
• :nucleus-application:detekt, ktlintCheck, apiDump (API dump committed)
• Windows: picker opened from a window is owned by it (modal, centered, stays above)
• Linux X11 and Wayland: portal picker attached to the window, export released afterwards
• macOS: picker still opens (unparented)