Improve error code handling in EmailPassword component

[coderabbitai]

Currently, the EmailPassword component uses string slicing to extract error codes from Firebase error messages:

const sliced = message.slice(32, message.length - 2);

This approach is fragile and could break if Firebase changes their error message format. We should implement a more robust error handling mechanism that:

1. Relies on Firebase's documented error code property
2. Implements proper error type checking
3. Handles user-friendly messages in a maintainable way

Related to PR: #1
Comment: cm090#1 (comment)