feat: created Email Template Builder UI

[nitingupta95]

Description

Added a new Email Template Builder component to the frontend.
This allows users to create email templates with subject, body, and placeholders like {{name}}.

Semver Changes

• Patch (bug fix, no new features)
• Minor (new features, no breaking changes)
• Major (breaking changes)

Issues

Closes #9 — Email Template Builder feature

Changes Made

• Added EmailBuilder.jsx component in frontend/src/components/
• Updated Campaign.jsx page to include the new builder
• Implemented basic input fields for subject, body, and variables
• Added initial styling and form handling

Checklist

• I have read the Contributing Guidelines
• My code follows the repository’s style guidelines
• I have added tests that prove my feature works
• I have added necessary documentation

[MD-IRFAN-RAJ]

@nitingupta95 resolve conflicts .also share screenshots of what you have changed.

[nitingupta95]

resovled the bug

[MD-IRFAN-RAJ]

@all-contrubutors please add @nitingupta95 for code

[MD-IRFAN-RAJ]

@all-contributors please add @nitingupta95 for code

[allcontributors]

@MD-IRFAN-RAJ

I've put up a pull request to add @nitingupta95! 🎉