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/linktree.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 448 512"><!--! 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="M16 173.4l125.8 0-89.4-85.4 49.5-51 85.2 87.8 0-124.8 73.9 0 0 124.8 85.2-87.6 49.4 50.8-89.4 85.2 125.7 0 0 70.5-126.4 0 90 87.6-49.3 49.8-122.2-123-122.2 123-49.5-49.6 90-87.6-126.4 0 0-70.5zM186.9 344.8l73.9 0 0 167.2-73.9 0 0-167.2z"/></svg>