Fix: Increase z-index of breadcrumb to prevent overlap

[ikumar200]

🐞 Bug

On the "Week Videos Listing" page, the breadcrumb bar was being overlapped by video cards, making the navigation hard to see or interact with i.e (the video completed green tick icon and the video icon at the bottom right corner)

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✅ Fix

Increased the z-index of the breadcrumb div container from z-10 to z-20 to ensure it appears above other elements.

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📂 File Modified

• src/components/CourseView.tsx

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🔗 Related Issue

Resolves #1861

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✔️ Checklist

• [x] I have performed a self-review of my code
• [x] There is no duplicate PR for this issue
• [x] Only the necessary file is changed (no lockfile or unrelated updates)
• [x] The UI works correctly after the fix