docs: add comprehensive documentation for callu-desktop application

[sarabekele30-cyber]

Summary

Hi @Sahnik0! I have created a detailed, dedicated README.md file specifically inside the callu-desktop directory as requested. It includes a breakdown of the Electron + Vite + TypeScript tech stack, core features, and local development setup instructions for the desktop application.

Related issue

Fixes #123

Changes

• Added comprehensive documentation for the desktop version in callu-desktop/README.md.

Testing

• Verified markdown structure locally.

Checklist

• I updated docs if needed.
• I verified the change locally.

[github-actions]

❌ PR validation failed.

Please fix the following before merging:

• Missing required Summary section in the PR body.
• Missing required Related issue section in the PR body.
• Missing required Changes section in the PR body.
• Missing required Testing section in the PR body.
• Add Fixes #123 in the PR body so the related issue is linked.

[github-actions]

❌ PR validation failed.

Please fix the following before merging:

• Missing required Summary section in the PR body.
• Missing required Checklist section in the PR body.

[github-actions]

❌ PR validation failed.

Please fix the following before merging:

• Missing required Summary section in the PR body.
• Missing required Checklist section in the PR body.

[github-actions]

✅ PR title, structure, and issue link validated.

[sarabekele30-cyber]

Hi @Sahnik0! Just wanted to let you know that all the PR validation checks have passed successfully and the conflicts are completely resolved. It's ready to be merged whenever you have a moment. Thank you!