bug: Completion badge overlaps sticky breadcrumb on course page while scrolling

[gaur777]

Describe the bug
On course pages, the green completion badge on completed week cards overlaps the sticky breadcrumb/topbar while scrolling.

To Reproduce

1. Open a course page with completed week cards
2. Scroll the card list upward
3. Observe that the green completion badge overlaps the sticky breadcrumb/topbar

Expected behavior
The completion badge should move under the sticky topbar together with the card and should not remain visible above the breadcrumb area.

Screenshots or GIFs
Attached:

• screenshot showing the bug where the completion badge overlaps the sticky breadcrumb/topbar
  
• screenshot showing the fixed behavior where the badge scrolls under the topbar
  

Info (please complete the following information):

• Browser: Google Chrome
• Version: 146.0.7680.178 (Official Build) (arm64)

Additional context
I investigated this locally and the fix appears to be a stacking-context issue between the sticky breadcrumb container and the completion badge overlay on course cards. I have verified a local fix and can submit it once the issue is assigned.