feat: add show/hide password toggle to login field

[gaidheal1]

Summary

Add an eye icon button to the password input field on the login page that toggles password visibility (show/hide hidden characters).

Acceptance Criteria

• Eye icon appears inside the password input field (trailing position)
• Clicking the icon toggles between type="password" (hidden) and type="text" (visible)
• Icon changes to reflect current state (e.g. eye / eye-slash)
• Works on both login and any other password fields (registration, password reset) if applicable
• Accessible: button has a descriptive aria-label (e.g. "Show password" / "Hide password")

Credit to Noodles