docs(login): recapture login section screenshots in English UI

Recaptured all login-section screenshots with English UI locale,
modal-element-only cropping (no full-page overlays), and PII redacted
via mosaic (username, email, role, Full Name, client IP).

Affected images (all 4 languages: en/ko/ja/th):
- signup_dialog.png
- signout_button.png
- forgot_password_panel.png
- menu_collapse.png
- my_account_information.png

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: nowgnuesLee