Rework post page (lead, pager), add skip link, unified focus ring, reduced motion and keyboard-accessible menu

Elternbeirat.Web/Components/Layout/MainLayout.razor.css

@@ -62,6 +62,12 @@
     color: var(--color-on-header);
 }
 
+/* On the blue gradient the global brand-blue focus ring would vanish; white
+   stays visible on both ends of it. */
+.brand:focus-visible {
+    outline-color: var(--color-focus-inverse);
+}
+
 /* The signet lives in its own component (Signet.razor), so its <svg> carries that
    component's scope attribute, not this one's; ::deep reaches it from here. */
 .brand ::deep .signet {
@@ -97,7 +103,9 @@
 }
 
 /* The hamburger button and its state checkbox are hidden on wide screens; the
-   media query below turns them on for narrow ones. */
+   media query below turns them on for narrow ones. display:none (beating the
+   global .visually-hidden the checkbox also carries) takes the checkbox out of the
+   tab order here, where there is no menu to open. */
 .nav-toggle,
 .nav-toggle-label {
     display: none;
@@ -205,6 +213,11 @@
     text-decoration: underline;
 }
 
+/* Same reason as the brand link in the header: a light ring on the dark band. */
+.footer-nav a:focus-visible {
+    outline-color: var(--color-focus-inverse);
+}
+
 /* Copyright: a thin rule separates it from the columns. The rule spans the content
    width, not the whole window, so it lines up with the columns above. */
 .footer-copyright {
@@ -228,6 +241,19 @@
         justify-content: space-between;
     }
 
+    /* The checkbox comes back as a real, focusable control -- only visually hidden
+       (global .visually-hidden), so Tab stops on it and Space toggles the menu. It
+       lives under the label, so the focus ring is drawn there instead. */
+    .nav-toggle {
+        display: block;
+    }
+
+    .nav-toggle:focus-visible + .nav-toggle-label {
+        outline: 3px solid var(--color-focus-inverse);
+        outline-offset: 2px;
+        border-radius: var(--radius);
+    }
+
     /* Show the hamburger button. */
     .nav-toggle-label {
         display: block;
@@ -271,20 +297,29 @@
         transform: translateY(-2px) rotate(-45deg);   /* back up by its own height */
     }
 
-    /* The nav takes its own row and is hidden until the checkbox is checked. */
+    /* The nav takes its own row and is hidden until the checkbox is checked.
+       max-height:0 alone would only hide it from the eye: its links would still
+       be Tab stops and still be read out. visibility:hidden takes them out of
+       both. Transitioning visibility delays the switch to hidden until the fold
+       has finished, so closing still animates. Opening uses the transition of the
+       :checked rule below, which leaves visibility out: the links must be Tab
+       stops the moment Space is pressed, not 0.2s later. */
     .main-nav {
         flex-basis: 100%;
         flex-direction: column;
         gap: 0;
         max-height: 0;
         overflow: hidden;
-        transition: max-height 0.2s ease;
+        visibility: hidden;
+        transition: max-height 0.2s ease, visibility 0.2s;
     }
 
     /* Checked state: reveal the stacked links. The max-height caps the open menu
        to the space below the sticky header; a longer list scrolls inside it
        instead of running off the screen. */
     .nav-toggle:checked ~ .main-nav {
+        visibility: visible;
+        transition: max-height 0.2s ease;
         max-height: 70vh;
         overflow-y: auto;
         margin-top: 0.5rem;