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/c.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 384 512"><!--! 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="M329.1 142.9c-62.5-62.5-155.8-62.5-218.3 0s-62.5 163.8 0 226.3 155.8 62.5 218.3 0c12.5-12.5 32.8-12.5 45.3 0s12.5 32.8 0 45.3c-87.5 87.5-221.3 87.5-308.8 0s-87.5-229.3 0-316.8 221.3-87.5 308.8 0c12.5 12.5 12.5 32.8 0 45.3s-32.8 12.5-45.3 0z"/></svg>