Portfolio screen

While multi-input may not be ideal for swift calculations, it's perfectly suited for maintaining portfolios.

Let's refer to it as the Portfolio screen since this moment.

We could refactor it in the following way:
- #31
- #32
- #33

Start by reading the related issues #31, #32, and #33 to understand the proposed refactoring of the multi-input flow. Use those issues to determine the intended Portfolio screen scope; the work is done only when that scope and the resulting screen behavior are clearly established.

Written by the indexing model from the issue text.