v0.12.3

Fixed

• The widget kept none of its script settings when embed.js was placed in
  the page <head>: it read document.currentScript only after
  DOMContentLoaded, when it is already null, so requests went to the
  wrong site. The script element is now captured while the script runs, with
  script[src*="/widget/embed.js"] as a fallback (#207).
• Pressing Enter or Tab while a mention search was still pending could insert
  an agent from the previous, stale result list. Keys are now held until the
  results for the current query arrive (#207).
• Ticket list accent colours fall back to the light preset when the host sets
  no theme.panel, and Guest/Create only offers the lookup form when both
  lookup_url and verification_url are present (#207).