Reject whitespace-only auth passwords

[ColumbusLabs]

/claim #743

Closes #4109

Summary

• Share an auth password schema between registration and login validators.
• Require passwords to contain at least eight non-whitespace characters.
• Preserve valid password values without trimming or rewriting the submitted string.

Manual demo (non-UI)

This is an auth validator fix, so the demo is the focused regression test behavior:

• registration rejects whitespace-only passwords that previously satisfied the raw 8-character minimum
• login rejects passwords with fewer than eight non-whitespace characters
• valid passwords are preserved exactly, without trimming or rewriting the submitted string

The focused test file exercises those paths and passes locally with:

node --test apps/api/src/tests/authValidators.test.js

Validation

• node --test apps/api/src/tests/authValidators.test.js
• node --test apps/api/src/tests/*.test.js
• node --check apps/api/src/validators/auth.js
• node --check apps/api/src/tests/authValidators.test.js
• git diff --check