fix: add email validation in Stay Updated newsletter form

[durgesh274]

Description

This PR fixes #631

Added email validation to the Stay Updated newsletter form in Footer.tsx. Previously, the form accepted any input (plain text, numbers, special characters) without any validation. Now users must enter a properly formatted email address before subscribing.

Notes for Reviewers

• Added isValidEmail regex validation function in the handleSubmit handler in Footer.tsx
• Added emailError state to store and display the validation error message
• Error message renders inline when invalid email is entered
• Error clears automatically as the user starts typing again
• Used noValidate on the form to disable browser's default validation popup and rely on custom error message instead
• Also fixed a pre-existingreact/no-unescaped-entities error on line 147 (You're → You're)

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