docs: add CHANGELOG.md to track version history and notable changes

[richachauhan15]

Description

This PR adds a CHANGELOG.md file at the project root to maintain a human-readable history of notable project changes and milestones.

Changes Made

• Added CHANGELOG.md following the Keep a Changelog format

• Added an [Unreleased] section for future updates

• Included Added, Changed, and Fixed categories

• Documented major project milestones, including:

  • Multi-AI support
  • Multi-platform publishing support (Dev.to, Hashnode, Medium, Webhooks)
  • Safari extension support via Xcode Web Extension Converter
  • Database support for the dashboard
  • Per-platform publishing status reporting
  • Python version lock to 3.12.3
  • Makefile, pytest, and Ruff integration
  • Architecture documentation and system flow diagram

Related Issue

Fixes #122

Type of Change

• Bug fix
• New feature
• Documentation update

Checklist

• My code follows project guidelines
• I have tested my changes
• Documentation updated if needed

[richachauhan15]

Hi @vanshaggarwal27 , I have completed the implementation and submitted a PR for review.
PR: #156
Thank you!

[vanshaggarwal27]

Please fix Lint error

[richachauhan15]

@vanshaggarwal27 please review it now

[vanshaggarwal27]

Lint test are still failing, please fix this

[richachauhan15]

@vanshaggarwal27