bug: integrated cart's frontend with backend+ other issues resolved

[indrasuthar07]

Description

• converted jsx files with tsx.
• Integrated frontend cart with backend cart API:
  # Frontend now syncs with the backend using cart.controller.ts endpoints.
  # Cart data is fetched, updated, and persisted on the server instead of localStorage only.
• Aligned frontend cart model with the backend structure (_id, productId, quantity, etc.)

Give a brief description of the pull request.

Semver Changes

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

Issues

#62

List any issues that this pull request closes.

Checklist

• I have read the Contributing Guidelines.

[04shubham7]

Looks Fine