Properly calculate page height to avoid scrolling behavior

In both `spu-ui` and in `qua-ui`, the available height seems to be calculated slightly incorrectly, leading to them having a scrolling layout that can hide part of the application. This is more noticeable on `qua-ui`:

Ideally, the page should not scroll, and all widgets should fit neatly on the available space, using scrolling frames only when actually intended.

Start by locating the page-height and layout calculations used by both `spu-ui` and `qua-ui`, then reproduce the issue in `qua-ui`, where it is more noticeable. Verify that the page itself no longer scrolls or hides application content, while scrolling frames still scroll when intentionally used.

Written by the indexing model from the issue text.