Improve wiki sidebar visual separation and spacing

What does this MR do and why?

Improve wiki sidebar visual separation and spacing This addresses user feedback about the sidebar and content feeling too close together and visually unclear after the sidebar was moved from right to left.

References

Screenshots or screen recordings

Before	After

Update: Fix Old Vs New UI

Old UI	New UI

How to set up and validate locally

MR acceptance checklist

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Related issue: #578646 (closed)