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/notdef.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="M64 390.3L153.5 256 64 121.7 64 390.3zM102.5 448L281.5 448 192 313.7 102.5 448zm128-192L320 390.3 320 121.7 230.5 256zM281.5 64L102.5 64 192 198.3 281.5 64zM0 48C0 21.5 21.5 0 48 0L336 0c26.5 0 48 21.5 48 48l0 416c0 26.5-21.5 48-48 48L48 512c-26.5 0-48-21.5-48-48L0 48z"/></svg>