Tall Harmonia dialogs overflow the viewport — header and Save/Cancel footer are unreachable

[NicoleNG18]

Description

A Harmonia dialog with enough fields to exceed the viewport height renders with its header pushed above the top edge and its Save/Cancel footer pushed below the bottom edge, both off-screen and unreachable. The dialog is vertically centered, so a body taller than the screen bleeds off both ends.

The most visible case is the document line-item editor (the "Add line" dialog on a header-items entity such as a Sales Invoice): with Product, Name, Quantity, Unit of Measure, Price, Discount Percent, Discount, Tax Rate, Vat Rate, Net, Vat and Total, the dialog is taller than the viewport and the Add/Save button cannot be clicked.

Steps to reproduce

1. Open a generated Harmonia application with a document (header-items) entity, e.g. a Sales Invoice.
2. Open an invoice and click to add a line item.
3. Observe: the "Add line" dialog title is scrolled off the top; the Save/Cancel footer is clipped at the bottom. The dialog body does not scroll, so the actions are unreachable.

Expected

The dialog should be capped to the viewport, with its body scrolling internally while the header and footer stay pinned and on screen — the same way the platform's Fundamental/BlimpKit IDE dialogs already behave.