40C3: tours, schedule data, tour map and calendar entries

- tour-map shortcode: Leaflet map of the tour locations with routes from the
  Congress, from the map/tours sections of data/schedule/<event>.yaml; Leaflet
  and the OSMIC, Maki and Temaki icon sets vendored; 39C3 uMap data converted.
- calendar shortcode: per tour date, a pill with an .ics download (iCalendar)
  and a Google Calendar link; Font Awesome Free vendored, fa-icon partial.
- README sections for the calendar and tour map shortcodes and the map data.

assets/vendor/fontawesome/brands/artstation.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><!--! Font Awesome Free 7.3.1 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2026 Fonticons, Inc. --><path fill="currentColor" d="M2.1 377.4l43 74.3c4.3 8.5 10.8 15.7 18.9 20.7s17.4 7.6 27 7.6l285.4 0-59.2-102.6-315.1 0zM501.9 350L335.7 59.3c-4.4-8.2-10.9-15.1-18.9-20S299.7 32 290.4 32l-88.4 0 257.3 447.6 40.7-70.5c1.9-3.2 21-29.7 2-59.1zM275.2 304.5l-115.5-200-115.5 200 231 0z"/></svg>