feat(security): implement cryptographic token signing wrapper

[Prateek2007-cmd]

Description

This PR resolves Issue 4: Missing Cryptographic Token Signing.
Closes #2250
The secure-storage.js utility previously used a very basic XOR cipher with a hardcoded key to obscure tokens in local storage. This offered virtually zero security against data tampering. This PR replaces the naive XOR obfuscation with a robust HMAC-SHA256 signature generated using the native Web Crypto API (window.crypto.subtle).

While client-side storage is inherently accessible to the user, this approach guarantees data integrity (tamper evidence) by invalidating any modified local storage entries and fulfills the technical requirement of the previously pending TODO.

Changes Made

• Implemented getKey(), signData(), and verifyData() utility functions using the window.crypto.subtle API.
• Updated SecureStorage.setItem to asynchronously generate an HMAC signature and store the payload and signature together.
• Updated SecureStorage.getItem to verify the signature of the payload before returning the data. If the signature is invalid, it logs a warning, purges the tampered data, and returns null.
• Removed the obsolete TODO: Implement cryptographic token signing wrapper comment.

Type of Change

• Security patch
• New feature

[vercel]

@Prateek2007-cmd is attempting to deploy a commit to the janavipandole's projects Team on Vercel.

A member of the Team first needs to authorize it.