Add API Server/panel/src/countries.js (the full world dataset, mirroring
the Web App's) with a countryGroups() helper, and have the OpenSky bbox
picker render every country grouped by continent instead of just Europe
plus a handful. Panel picker now offers 177 countries (European, Asian,
African, North/South American, Oceanian) alongside World, Continents and
Custom.
Verified live: Plugins → OpenSky → Configure shows the grouped list.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>