Cannot exit fullscreen gadget on mobile — requires Escape key

[aethernet]

Problem

When a gadget is in fullscreen mode, exiting requires pressing the Escape key. On mobile devices, there is no Escape key available (mobile keyboards don't include it), making it impossible to exit fullscreen mode on mobile.

This effectively traps the user in the fullscreen gadget view with no way to get back to the normal workspace.

Expected behavior

There should be a visible on-screen button (e.g. a close/exit "×" or a back button) to exit fullscreen gadget mode, so it works on devices without a physical keyboard.

Context

• This is a mobile-specific issue — desktop users can press Escape as expected.
• Related to Workspace view is not responsive: gadget panel clipped, chat squeezed on phones #64 (general mobile responsiveness of the workspace view).
• The fix should be straightforward: add a visible exit affordance in addition to the Escape key handler.