fix(auth): prevent crash when Google OAuth email is missing

[KanhaiyaPandey]

Summary

Fixes an issue in the Google OAuth strategy where the code directly accessed
profile._json.emails[0].value without validating that emails exists and
contains at least one entry.

If Google does not return an email array, this results in:
TypeError: Cannot read property '0' of undefined

This PR adds proper validation and ensures the OAuth flow fails gracefully
instead of crashing.

Changes

• Added safe check for profile.emails (or _json.emails) before accessing index 0
• Extracted email into a primaryEmail variable
• If no email is found, return:
  done(null, false, { msg: 'Google account does not provide an email address.' })
• Replaced all direct usages of profile._json.emails[0].value

Why This Is Needed

Google does not guarantee that the emails array will be present
(depending on scopes, account type, or privacy settings).
Without validation, the OAuth flow crashes instead of failing gracefully.

Testing

• Mocked a Google profile without emails
• Confirmed OAuth flow no longer throws a TypeError
• Verified user-friendly failure message is returned instead

Closes #3907