Add the design foundation: self-hosted Nunito, type scale, new tokens and an Icon component

Elternbeirat.Web/Shared/Icon.razor

@@ -0,0 +1,13 @@
+@*
+    Renders one icon from IconSet as inline SVG. Purely decorative: aria-hidden hides
+    it from screen readers (the text next to it carries the meaning) and
+    focusable="false" keeps old Edge/IE from putting it in the tab order. The stroke
+    is currentColor, so the icon takes the colour of the surrounding text. An unknown
+    name renders nothing at all.
+*@
+@if (_markup is not null)
+{
+    <svg class="icon" width="@Size" height="@Size"
+         viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"
+         stroke-linecap="round" stroke-linejoin="round" aria-hidden="true" focusable="false">@_markup</svg>
+}