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/bluesky.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 576 512"><!--! 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="M407.8 294.7c-3.3-.4-6.7-.8-10-1.3 3.4 .4 6.7 .9 10 1.3zM288 227.1C261.9 176.4 190.9 81.9 124.9 35.3 61.6-9.4 37.5-1.7 21.6 5.5 3.3 13.8 0 41.9 0 58.4S9.1 194 15 213.9c19.5 65.7 89.1 87.9 153.2 80.7 3.3-.5 6.6-.9 10-1.4-3.3 .5-6.6 1-10 1.4-93.9 14-177.3 48.2-67.9 169.9 120.3 124.6 164.8-26.7 187.7-103.4 22.9 76.7 49.2 222.5 185.6 103.4 102.4-103.4 28.1-156-65.8-169.9-3.3-.4-6.7-.8-10-1.3 3.4 .4 6.7 .9 10 1.3 64.1 7.1 133.6-15.1 153.2-80.7 5.9-19.9 15-138.9 15-155.5s-3.3-44.7-21.6-52.9c-15.8-7.1-40-14.9-103.2 29.8-66.1 46.6-137.1 141.1-163.2 191.8z"/></svg>