v1.18.0 — switch to Standard from the account card

• Signed in on a free engine, the options page account card offers "Switch to Standard".
• Sign-in hints open the sign-in form on openimmersive.ai.
• The popup links URLs in its status line.
• No permission changes. Tests: 253/253, including a new account-card suite.

Install: Chrome Web Store, Firefox Add-ons, Microsoft Edge Add-ons (links in the README). Store updates roll out as each store finishes review.