docs: improve CHANGELOG.md structure and contributor guidance

[srinithithirumaran]

Description

This PR improves the existing CHANGELOG.md by aligning it more closely with the Keep a Changelog format and enhancing contributor guidance for maintaining future project updates.

Related Issue

Closes #1478

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📝 Documentation update
• 🎨 Style / UI improvement
• ♻️ Refactor (no functional changes)
• ⚡ Performance improvement
• 🧪 Test addition or update
• 🔧 Chore / Tooling / Config

Changes Made

• Improved the Unreleased section by adding standard changelog categories (Added, Changed, Fixed, Documentation, and Security).
• Enhanced contributor guidance with clearer instructions for updating the changelog.
• Added release process and Semantic Versioning guidance to improve maintainability and documentation consistency.

Screenshots (if applicable)

N/A (Documentation-only changes)

Testing

• I have tested these changes locally
• I have added/updated tests where applicable
• All existing tests pass

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my own code
• I have commented my code where necessary
• I have updated the documentation if needed
• My changes generate no new warnings or errors

[vercel]

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