Enhancement: Display Success Message After Subscription

[akshay0611]

Changes Introduced:

• Added a success message (✅ Subscription successful!) that appears when a user subscribes.
• Implemented JavaScript logic to display the message dynamically.
• Cleared the email input field after a successful subscription.

How It Works:

1. When a user enters an email and clicks "Subscribe," a success message appears.
2. The email field is cleared after submission.
3. The message is hidden initially and only displays after a valid entry.

---

Test Instructions:

1. Enter an email in the input field.
2. Click "Subscribe."
3. Verify that the success message appears.
4. Ensure the email input field is cleared after submission.

---

Related Issue

Closes [#17 )