The earlier editor-only zoom implementation in #32860 rendered the
active pane with padding, a border, rounded corners, and a shadow. In
addition to keeping docks visible, that treatment made the transient
editor zoom mode apparent.

The current `ToggleEditorZoom` implementation (#53911) only omits
sibling panes from the pane group, without any visual indication.
Without a persistent control or decoration, the result can look like an
ordinary single-pane layout, so users cannot tell whether toggling the
command will restore hidden splits.

So this commit renders the maximized pane as an inset card with padding,
a subtle theme border, rounded corners, and a shadow. Keeping this
treatment in `PaneGroup` makes it apply only to editor zoom, leaves
docks untouched, and distinguishes it from `ToggleZoom`'s square
workspace overlay.

## Showcase

<img width="862" height="415" alt="Screenshot 2026-07-15 at 18 51 30"
src="https://github.com/user-attachments/assets/f61c61ce-79b7-4e3a-a9c4-0775931fa90d"
/>

---

Release Notes:

- N/A

---------

Co-authored-by: Danilo Leal <daniloleal09@gmail.com>