[Bug]: Context row under the composer is a square slab stuck to the card #36258

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/web

Steps to reproduce

1. In Settings > Appearance > Advanced, turn on "Keep composer context visible".
2. Open a started thread in a Git project, so the row with the workspace and branch shows under the composer.
3. Scroll the conversation so content (an image makes it obvious) sits behind that row.

Expected behavior

The row's background is a rounded pill with a small gap between it and the composer card. It keeps the page-coloured glass from #34846, so it is still invisible over an empty page and its labels stay readable over scrolling chat. The composer card and the row's labels stay exactly where they are today; only the background's shape changes.

Actual behavior

Since #34846 the row has a page-coloured glass background that is a full-width rectangle with square corners, pressed directly against the rounded composer card. Over an empty page it is invisible, but over any content it shows as a hard-edged slab under the card.

Impact

Cosmetic issue

Version or commit

main at 350753a

Environment

Web dev client in Chromium, Windows 11, dark theme, 1280x800. A gradient block is placed behind the composer to stand in for a thread image.

Workaround

None. A fix is proposed in #36259.