refactor: use english for routes, parameters and internal messages

templates/board/plan/_spot.html.twig

@@ -1,6 +1,6 @@
 {#
     The shared shape a plan is drawn from. Imported by each board/plan/_<type>.html.twig, so the
-    per-type partials carry geometry only and free/belegt/deine looks identical everywhere.
+    per-type partials carry geometry only and free/taken/yours looks identical everywhere.
 
     Clicking always opens a modal: the create modal when free, the edit modal when it is yours
     (which is where changing the times and releasing live). Nothing else is clickable, so the SVG