Guide on Submenus (Toolbar + Menu)

Thank you for the great documentation on creating new toolbars.

Here is another useful example:

The command class (which is added via `addCommand()`) has an optional function named `GetCommands(self) -> list[str]`. You can return a list of command names to be grouped together. This new Group-Command can be used similar to a normal command item, but:
- In a toolbar it will display a drop-down list (like the Constraints or Circle combo menu).
- As a menu-item it will create a menu entry with all selected commands as submenu items.

There is also `GetDefaultCommand(self) -> int` which will trigger the command at chosen index (e.g. if user clicks on toolbar combo box without opening the drop-down).

The group can implement `Activated(self, cmd: int = 0) -> None` which provides the index of the performed action. If the group does *NOT* implement `Activated()`, the `Activated()` function of the child command is executed. If the group *does* implement `Activated()`, then the child is not called and the group is responsible for handling the action.

`CmdType` rules apply to the group first. E.g. if child command can be shown in edit mode, but group cannot, then you wont be able to call any child because the group will be deactivated.

...

As a related question: how to find valid menu names? E.g. I tried "Geometries" and it inserts a new menu item at the end of the "Sketch" menu. While this is where I *want* it to be, it is not where I would have *expected* the item to appear. I know the documentation says "names an entry, not a menu", but I dont know how to get either except by trial and error. Using an entry of a menu to append to that menu feels wrong, but I guess it is how it is.

Start by locating the existing documentation on creating toolbars and reviewing the FreeCAD command APIs mentioned in the issue. Add a guide covering GetCommands(), GetDefaultCommand(), Activated(), CmdType behavior, and how menu names and entries determine submenu placement; validate the examples and menu behavior in FreeCAD.

Written by the indexing model from the issue text.