Refresh header and footer with signet, gradient, nav pills and three-column footer; fix box-sizing of design boxes

Elternbeirat.Web/Features/Layout/FooterYear.cs

@@ -0,0 +1,35 @@
+namespace Elternbeirat.Web.Features.Layout;
+
+/// <summary>
+///     Works out the year shown in the footer's copyright line.
+/// </summary>
+/// <remarks>
+///     The container runs on UTC, but visitors live in Germany. Taking the year
+///     straight from the server clock would show the old year for the first hour
+///     (two in summer time) of every new year, so the instant is converted to
+///     Europe/Berlin first.
+/// </remarks>
+public static class FooterYear
+{
+    /// <summary>
+    ///     IANA id; resolves on every platform .NET supports, Windows included.
+    /// </summary>
+    private static readonly TimeZoneInfo Berlin =
+        TimeZoneInfo.FindSystemTimeZoneById("Europe/Berlin");
+
+    /// <summary>
+    ///     Returns the calendar year in Berlin at the given instant.
+    /// </summary>
+    /// <param name="now">
+    ///     The current instant, in any offset; usually
+    ///     <see cref="TimeProvider.GetUtcNow"/>.
+    /// </param>
+    /// <returns>The year a visitor in Germany would see on their calendar.</returns>
+    /// <example>
+    ///     <code>
+    ///         FooterYear.For(new DateTimeOffset(2026, 12, 31, 23, 30, 0, TimeSpan.Zero)); // 2027
+    ///     </code>
+    /// </example>
+    public static int For(DateTimeOffset now) =>
+        TimeZoneInfo.ConvertTime(now, Berlin).Year;
+}