fix: improve DBusMenu compatibility on XFCE

[pitill0]

Summary

Improve the Linux StatusNotifierItem DBusMenu implementation so tray context menus are correctly exposed on XFCE.

XFCE does not invoke the StatusNotifierItem ContextMenu method for a normal right click. Instead, its StatusNotifier plugin builds a local menu from the exported com.canonical.dbusmenu object. The previous implementation exposed only a subset of that interface, causing XFCE to consider the menu unusable and fall back to the panel context menu.

Changes

• Expand the DBusMenu interface with:

  • GetGroupProperties
  • GetProperty
  • EventGroup
  • AboutToShowGroup
  • ItemsPropertiesUpdated
  • LayoutUpdated
  • ItemActivationRequested

• Return False from AboutToShow when the static layout does not require an update.

• Add property filtering and shared menu event dispatching.

• Extend tray tests to cover the DBusMenu contract.

• Fix the Web JavaScript metadata test so it explicitly injects navigatorRef under Node.js.

• Check the browser entrypoint as an ES module in the local gate.

• Make the development environment reproducible by including Bandit in the dev dependencies and using .[dev] from requirements-dev.txt.

Validation

Tested on XFCE 4.18.4 under Xorg.

Before the change:

• left click correctly activated FluxTuner
• middle click generated SecondaryActivate
• right click opened the XFCE panel context menu
• XFCE detected Menu=/MenuBar, but did not build a usable application menu

After the change:

• left click continues to activate FluxTuner
• right click correctly opens the FluxTuner context menu
• full make gate passes cleanly

Note: XFCE may require a panel reload (xfce4-panel -r) to refresh a newly registered tray icon in some sessions. This appears to be separate from the DBusMenu compatibility issue addressed here.