feat: replace divs with semantic ul/li on Topics page for improved accessibility

[arbirali]

Description

Replaced non-semantic <div> elements with proper semantic <ul> and <li> tags for the list structure on the Topics page. This improves the accessibility of the page by ensuring screen readers and assistive technologies can correctly interpret and navigate the list content.

This change aligns with [WCAG 1.3.1 – Info and Relationships](https://www.w3.org/WAI/WCAG21/Understanding/info-and-relationships.html), which requires that structure and relationships in content be programmatically determined.

Related GitHub Issue: [tutor-indigo/#146 – Accessibility compliance](overhangio/tutor-indigo#146)
Taiga Ticket: [US 106 – Replace div with semantic ul/li on Topics page](https://tree.taiga.io/project/zaraahmed-tutor-indigo-accessibility/us/106)

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How Has This Been Tested?

• Verified that the semantic structure is correctly rendered in the DOM.
• Used keyboard navigation and a screen reader to ensure list items are read and navigated as expected.
• Confirmed no visual or functional regressions were introduced.

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Screenshots/sandbox (optional):

Live Preview: [Topics Page – Demo Course](https://apps.sandbox.openedx.edly.io/discussions/course-v1:OpenedX+DemoX+DemoCourse/topics)

Before	After
Non-semantic div-based list	Proper ul/li list structure

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Merge Checklist

• If your update includes visual changes, have they been reviewed by a designer? Send them a link to the Sandbox, if applicable.
• Is there adequate test coverage for your changes?

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Post-merge Checklist

• Deploy the changes to prod after verifying on stage or ask @openedx/edx-infinity to do it.
• 🎉 🙌 Celebrate! Thanks for your contribution.

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Let me know if you need help drafting a related changelog or internal documentation note.

[codecov]

Codecov Report

Attention: Patch coverage is 76.92308% with 6 lines in your changes missing coverage. Please review.

Project coverage is 93.09%. Comparing base (ac471e2) to head (3bc1cb5).

Files with missing lines	Patch %	Lines
src/discussions/posts/post/PostLink.jsx	83.33%	2 Missing and 1 partial ⚠️
...c/discussions/in-context-topics/TopicPostsView.jsx	50.00%	1 Missing ⚠️
src/discussions/posts/PostsView.jsx	0.00%	1 Missing ⚠️
src/discussions/topics/TopicsView.jsx	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #773      +/-   ##
==========================================
- Coverage   93.15%   93.09%   -0.06%     
==========================================
  Files         161      161              
  Lines        3402     3404       +2     
  Branches      919      921       +2     
==========================================
  Hits         3169     3169              
- Misses        216      217       +1     
- Partials       17       18       +1     

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[awais-ansari]

Please update the test cases. The required checks are failing. Other than that, the changes look good to me.