[demolaf]

Keeps the original Firebase error on FirebaseUIError and warns about configuration errors, so a translated message no longer hides the real cause.

Changes

• FirebaseUIError keeps the original FirebaseError as cause, so apps can log or report the untranslated message.
• handleFirebaseError logs Firebase configuration error codes, such as auth/api-key-expired, with console.warn.
• Documents both in the README Error messages section.

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Maintainer note: Fixes internal CPRN-594

[gemini-code-assist]

Code Review

This pull request updates FirebaseUIError to retain the original Firebase error as its cause and introduces warning logs for configuration-related errors. Corresponding unit tests and documentation updates have also been added. Feedback on these changes suggests optimizing the configuration error code lookup by using a Set instead of an array, handling already-wrapped FirebaseUIError instances in handleFirebaseError to prevent double-wrapping and duplicate warnings, and adding a test case to verify this behavior.