[Bug]: Provider model submenu overlaps the parent provider menu

[ifBars]

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. Open a thread in the web UI.
2. Open the provider/model selector in the composer footer.
3. Hover an available provider with a nested submenu, such as Claude.
4. Observe the submenu position relative to the parent provider list.

Expected behavior

The nested submenu should open adjacent to the parent provider menu without overlapping it, while still feeling visually attached like a standard nested desktop menu.

Actual behavior

The nested submenu overlaps the parent provider menu, which makes the control look visually awkward and broken.

Impact

Cosmetic issue

Version or commit

main

Environment

Windows desktop app, Bun 1.3.5

Logs or stack traces

N/A

Screenshots, recordings, or supporting files

Workaround

N/A