orb 0.3.0-rc5

AppImage desktop launch fixes:
- GUI double-click runs headless + opens the dashboard in the browser
  (no longer exits immediately on missing terminal).
- xdg-open no longer inherits the AppImage's LD_LIBRARY_PATH.
- Reopens the last-loaded project on launch.

Also: CI test_python/test_rust green, mkdocs --strict fixed.