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/digital-ocean.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="M87 481.8l73.7 0 0-73.6-73.7 0 0 73.6zM25.4 346.6l0 61.6 61.6 0 0-61.6-61.6 0zM491.6 176.9C468.6 102.7 409.2 43.6 335 20.3 164.9-32.8 8 93.7 8 255.9l95.8 0c0-101.8 101-180.5 208.1-141.7 39.7 14.3 71.5 46.1 85.8 85.7 39.1 107-39.7 207.8-141.4 208l0 .3-.3 0 0 95.8c162.6 0 288.8-156.8 235.6-327.1zm-235.3 231l0-95.3-95.6 0 0 95.6 95.3 0 0-.3 .3 0z"/></svg>