improve: enhance pull request template structure

[YLaxmikanth]

Closes #17

Summary

This PR improves the existing pull request template by introducing a cleaner structure, clearer contributor guidance, improved testing sections, and a more organized review workflow.

The goal is to make pull request submissions more consistent, readable, and reviewer-friendly while maintaining the lightweight style of the repository.

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Improvements Made

• Added better section organization and formatting
• Improved readability using separators and grouped sections
• Added categorized change types
• Added reviewer notes section
• Improved testing and browser verification structure
• Added optional accessibility checklist
• Added optional documentation checklist
• Improved screenshots/demo section layout
• Enhanced contributor guidance throughout the template

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Benefits

• Improves contributor onboarding experience
• Standardizes PR submissions
• Reduces review confusion
• Makes reviews faster and easier
• Encourages better testing and documentation practices
• Improves overall repository workflow consistency

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Testing

• Markdown preview verified locally
• Template formatting checked
• Checklist rendering verified