feat: add onMenuOpened callback to Tray composable

[kdroidFilter]

Summary

Closes #233

• Add onMenuOpened: (() -> Unit)? = null parameter to all Tray() composable overloads
• On Linux, hooks into the DBusMenu AboutToShow protocol to detect when the menu is about to open
• Noop on Windows and macOS (parameter accepted but ignored)
• Includes LayoutUpdated-based suppression to prevent infinite feedback loops when the callback mutates Compose state
• Build script now invalidates the ~/.cache/composetray/ native library cache to avoid stale .so issues

API usage

Tray(
    icon = Icons.Default.Cloud,
    tooltip = "My App",
    onMenuOpened = {
        // Refresh data when menu opens
        serviceStatus = pollRemoteService()
    },
) {
    Item("Status: $serviceStatus")
}

Test plan

• Linux: verify callback fires once per menu open, counter increments in main window
• Linux: verify no infinite loop when callback mutates state
• Linux: verify counter stays at 0 until user actually opens menu (not on startup)
• Windows/macOS: verify no regression (parameter is noop)
• GraalVM native-image: verify no additional metadata needed