Odoo can now hide or show menu entries based on business conditions, such as the companies a user can access. This helps keep navigation cleaner and more relevant for each user without custom workarounds.

This commit adds the ability to conditionally render menus.

This is done by adding a new field: `web_invisible`. Note that, this field accepts Python expressions.

task-id: 4250356

The Gantt view is easier to work with thanks to more compact rows, steadier drag behavior, and faster creation when selecting time cells. Planning users also get smoother shift splitting because split controls no longer interfere with dragging scheduled items.

We improve the gantt view in several aspects:
- the height of rows is a bit reduced so that more data is visible
- the pills do not rotate when dragged
- the form dialog is directly opened when one or several cells are selected by drag and drop
- (planning) the splitting tools do not block the drag and drop of pills anymore

Task ID: 4350819

Follow-up levels that assign activities to salespeople now create activities for every salesperson linked to the invoices in the follow-up. This helps ensure all responsible salespeople are notified, reducing missed follow-up actions when several salespeople are involved.

When a follow-up level is set to create an activity to Salespeople, it now creates an activity to all Salespersons from all Invoices part of the follow-up. Where before an activity would only be created for one SSalespersons.

Task: 4374391

Document-related settings are simplified so new spreadsheets go to My Drive, Sign uses its standard Sign folder, and Projects can choose where company project folders are created. Labels and defaults are updated to make document storage easier to understand and reduce empty or confusing settings sections.