refactor: migrate Divider component from deprecated makeStyles to MUI v5 styled API

[DevaanshKathuria]

Description

Migrates src/globalComponents/Divider.jsx from deprecated @mui/styles makeStyles to MUI v5 styled() API as part of #314.

Related Issue

Part of #314

Motivation and Context

The Divider component was using makeStyles from @mui/styles which is deprecated in MUI v5. Replaced with three styled components: Container, Border, and Content; zero functional or visual changes.

How Has This Been Tested?

• Ran npm run dev successfully
• No new console errors introduced
• No visual regression

Screenshots or GIF (In case of UI changes):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.