feat: added google oauth signup/login functionality

[iemio]

Pull Request for Stock Analyzer

Issue Title

Add Google OAuth Signup/Login Functionality

Contributor Details

• Name: Keshav
• GitHub ID: iemio
• Participation Program (if any): GSSOC

Related issues

Closes #37

Changes

• Add "Login with Google" button on the signup & login page
• Google OAuth login/signup using Firebase Auth
• Store user info (name, email, UID) securely Display logged-in user's name in the navbar/header
• Show logout button

Files changed

Login.js, signup.js, Login.css, Signup.css

Type of Change

• Bug fix (fixes an existing issue)
• New feature (adds new functionality)
• Code style update (formatting, refactoring)
• Breaking change (may affect existing features)
• Documentation update

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Checklist

• My code follows the project’s guidelines and best practices.
• I have performed a self-review of my code.
• I have added meaningful comments where necessary.
• I have updated documentation wherever applicable.
• My changes do not generate any new warnings or errors.
• I have included screenshots, graphs, or test logs (if applicable).
• Any dependent changes have been merged and documented.

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[github-actions]

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[SrigadaAkshayKumar]

Have you added a ‘Login with Google’ button on the login page?

[iemio]

Yes, I have added.

[SrigadaAkshayKumar]

@iemio drop your email here it is necessary for gssoc points

[iemio]

@SrigadaAkshayKumar keshavkumar017290@gmail.com