fix(desktop): round main area top corners

[ComputelessComputer]

Keep top corners on the edge-to-edge main surface and cover the scaffold class override.

---

This is part 2 of 3 in a stack made with GitButler:

•  3  fix(desktop): add display language setting #5369
•  2  fix(desktop): round main area top corners #5371 👈
•  1  feat(desktop): add sidebar timeline setting #5366

---

Note

Low Risk
Desktop layout/CSS-only change with no auth, data, or API impact.

Overview
For the edge-to-edge / top main surface chrome, the shell no longer forces the main chat anchor to be fully square. It now applies rounded-t-xl and rounded-b-none on [data-chat-floating-anchor] (replacing rounded-none), so the main area keeps rounded top corners while staying flush on the bottom and sides.

The MainShellScaffold edge-to-edge test was updated to assert the new descendant rounding classes alongside the existing border overrides.

^{Reviewed by Cursor Bugbot for commit 7392f23. Bugbot is set up for automated code reviews on this repo. Configure here.}

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit b312eeb. Configure here.}