[JulienVannier66]

What does this PR do?

Small design system fixes, one commit per ticket:

• Side panel: OSS::SidePanel checks clicks against its own root element instead of the first .oss-side-panel in the document. With two side panels mounted (campaign Settings keeps a hidden tracking plan selector, then the duplicate campaign modal opens its own), a click inside the second panel was seen as outside and closed it.
• Button dropdown: the OSS::ButtonDropdown menu clips its content (overflow: hidden), so the item hover background follows the rounded corners. Every current usage only renders simple rows, nothing needs to overflow the menu.
• Sidebar: the menu shown when hovering a group of the collapsed sidebar gets a gray-200 border.

Related to:

• https://linear.app/upfluence/issue/VEL-7132/cant-assign-tracking-plan-from-duplicate-campaign-modal-while-user-is
• https://linear.app/upfluence/issue/VEL-7009/non-rounded-edges-in-context-menu-for-brand-pre-made-searches
• https://linear.app/upfluence/issue/VEL-7000/no-visible-upper-limit-on-the-menu-when-hovering-collapsed-navbar

What are the observable changes?

Visible in the apps once @upfluence/oss-components is released and bumped.

• Workflow > campaign with a tracking plan > Settings > Settings > quick navigation > duplicate a campaign > enable "Track orders & Sales performances" > Select an existing tracking plan > click a plan's radio: the side panel stays open and the plan is selected.
• Search > brand pre-made searches "…" menu: hovering the first or the last option shows a rounded hover background.
• Collapsed sidebar: hovering a group shows its menu with a light gray border.

Good PR checklist

• Title makes sense
• Is against the correct branch
• Only addresses one issue
• Properly assigned
• Added/updated tests
• Added/updated documentation with Figma design link. Don't forget to replace "design" by "file" in the URL. For example https://www.figma.com/file/example
• Migrated touched components to Glimmer Components
• Properly labeled

[linear-code]

VEL-7000

VEL-7009

VEL-7132