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/solid/diagram-next.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="M384 224c35.3 0 64-28.7 64-64l0-64c0-35.3-28.7-64-64-64L64 32C28.7 32 0 60.7 0 96l0 64c0 35.3 28.7 64 64 64l128 0 0 64-32 0c-6.5 0-12.3 3.9-14.8 9.9s-1.1 12.9 3.5 17.4l64 64c6.2 6.2 16.4 6.2 22.6 0l64-64c4.6-4.6 5.9-11.5 3.5-17.4S294.5 288 288 288l-32 0 0-64 128 0zM64 288c-35.3 0-64 28.7-64 64l0 64c0 35.3 28.7 64 64 64l320 0c35.3 0 64-28.7 64-64l0-64c0-35.3-28.7-64-64-64l-34 0c5.6 21.7-.5 45.1-16.7 61.3l-64 64c-25 25-65.5 25-90.5 0l-64-64C98.6 333.1 92.4 309.7 98 288l-34 0z"/></svg>