Add Piggy Bank savings feature with modal, validation, and toggle view

[Ramankumar120]

Piggy Bank Feature

• Added Piggy Bank savings card
• Modal-based Add Money flow
• Input validation with UI feedback
• View / Hide savings toggle
• Data persistence using localStorage

Fixes #106

[vercel]

@Ramankumar120 is attempting to deploy a commit to the Renu's projects Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions]

🎉 Thanks for the PR, @Ramankumar120!

We really appreciate you taking the time to contribute to OpenPlayground! 💙

---

⭐ Love this project?

Please give us a star! It helps the project grow and reach more developers! 🌟

🔗 https://github.com/Renu-code123/ExpenseFlow

---

✅ PR Checklist

Before we review, please ensure:

• Your code follows the project's coding standards
• All file changes are accurate and intentional
• You've tested your changes locally
• Any review comments have been addressed

---

🙌 Thank You for Contributing!

We truly appreciate your interest in contributing to this project.

• Please make sure your code follows the project structure
• Add clear commit messages and comments where necessary
• Ensure your changes do not break existing functionality

We'll review your PR as soon as possible. Keep up the great work! ✨

---

[Ramankumar120]

I’ve cleaned up the branch and removed all unrelated changes
(server.js, package-lock.json, node_modules).

Only the frontend Piggy Bank feature is included now.
The branch is clean locally — please refresh conflicts.

[Renu-code123]

@Ramankumar120, resolve the conflict and add a screenshot of before or after changes