feat(centralui): adopt Theme 0.5.3 ScrollNav rail scroll pane (#61)

Bump ZB.MOM.WW.Theme 0.5.0 -> 0.5.3, set ThemeShell ScrollNav=true, drop
NavMenu's own .rail-scroll wrapper and the site.css rail scroll block
(keeps .rail-updates*). NavMenu test now asserts no local wrapper.

Claude-Session: https://claude.ai/code/session_01GT67ACmpMR7b9LGRPLijMi

tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Layout/NavMenuTests.cs

@@ -254,23 +254,19 @@ public class NavMenuTests : BunitContext
     }
 
     /// <summary>
-    /// ThemeShell's <c>nav.side-rail</c> never fills the sticky 100vh rail, so
-    /// a long expanded nav grows past the viewport and pushes
-    /// <c>.rail-foot</c> off-screen. <c>NavMenu</c> wraps its items in a
-    /// <c>div.rail-scroll</c> pane that <c>site.css</c> makes scroll on its
-    /// own (lg+), leaving the brand bar and rail footer pinned. This asserts
-    /// the wrapper exists and actually contains the nav sections, not just
-    /// that the class string appears somewhere in the markup.
+    /// The rail scroll pane is owned by the kit (ThemeShell ScrollNav="true",
+    /// Theme 0.5.3). NavMenu must not add its own <c>.rail-scroll</c> wrapper,
+    /// or the rail gets two nested scroll panes.
     /// </summary>
     [Fact]
-    public void NavItems_RenderInsideTheRailScrollPane()
+    public void NavItems_DoNotCarryTheirOwnRailScrollWrapper()
     {
         var cut = RenderWithRoles("Administrator", "Designer", "Deployer");
 
         cut.WaitForAssertion(() =>
         {
-            Assert.Contains("class=\"rail-scroll\"", cut.Markup);
-            Assert.NotEmpty(cut.FindAll("div.rail-scroll details.rail-section"));
+            Assert.NotEmpty(cut.FindAll("details.rail-section"));
+            Assert.DoesNotContain("rail-scroll", cut.Markup);
         });
     }
 }