Purpose

Adds SameSite=None; Secure to every WordPress authentication cookie so REST requests originating from extrachill.link carry logged-in identity when hitting artist.extrachill.com.

Behavior

• ec_register_cookie_samesite_callback() hooks into init (priority 1).
• Registers ec_add_samesite_none_to_wordpress_cookies() with header_register_callback() so it runs immediately before headers are sent.
• Iterates over every Set-Cookie header, targets only values containing wordpress_, and appends SameSite=None; Secure unless already present.

User Impact

Users managing artist link pages on extrachill.link stay authenticated when the interface polls /extrachill/v1/artists/{id}/permissions, ensuring edit buttons reflect accurate access without forcing re-login.