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

src/ZB.MOM.WW.ScadaBridge.CentralUI/wwwroot/css/site.css

@@ -171,27 +171,6 @@
     --sb-backdrop: rgba(0, 0, 0, 0.6);
 }
 
-/* ── Rail nav scroll pane ────────────────────────────────────────────────
-   ThemeShell's nav.side-rail is a flex column inside the sticky 100vh
-   #theme-rail (lg+), but it never fills that height and nothing inside it
-   scrolls, so a long nav grows past the viewport and carries the footer
-   with it. Fill the rail and let the nav items (NavMenu's .rail-scroll
-   wrapper) scroll while the brand bar and .rail-foot stay put. Below lg the
-   rail is inline and scrolls with the page, so the rule is scoped to lg+.
-   The kit is untouched (deferred-work register: upstream into
-   ZB.MOM.WW.Theme so the other consumers get it too). */
-@media (min-width: 992px) {
-    #theme-rail > .side-rail {
-        height: 100%;
-    }
-    .rail-scroll {
-        flex: 1 1 auto;
-        min-height: 0;
-        overflow-y: auto;
-        overscroll-behavior: contain;
-    }
-}
-
 /* ── Rail pending-updates indicator ──────────────────────────────────────
    Sits in .rail-foot just above .rail-user. One line when quiet, two when
    something is pending; tokens only so dark mode follows for free. */