style(ui): align admin styling with ScadaLink master conventions

- Move CSS into wwwroot/css/ (theme.css, site.css); sidebar 218 -> 220px
- Add hamburger + Bootstrap collapse for <lg viewports
- Add Components/Shared/ with LoadingSpinner, ToastNotification, StatusBadge
- Replace .page-title with flex + <h4 class="mb-0"> across 20 pages
- Convert NewCluster + IdentificationFields forms to card + h6 subsection pattern

src/Server/ZB.MOM.WW.OtOpcUa.Admin/Components/Shared/StatusBadge.razor

@@ -0,0 +1,7 @@
+@* Status chip — wraps the theme.css .chip / .chip-ok / .chip-warn / .chip-bad / .chip-idle classes. *@
+<span class="chip @CssClass">@Text</span>
+
+@code {
+    [Parameter] public string Text { get; set; } = "";
+    [Parameter] public string CssClass { get; set; } = "chip-idle";
+}