refactor(admin): compact UI styling for data-dense admin interface

- Reduce table cell padding (px-5 py-4 → px-3 py-2) across OrderTableBody, ProductTableBody, StopTableBody, AdminTable
- Narrow sidebar (w-60 → w-56) with smaller nav items
- Reduce page/card padding in admin-design-system.css
- Smaller default buttons (md → sm) in AdminButton
- Smaller page headers (text-2xl → text-xl, w-12 → w-10 icon)
- Tighter cards and filter tabs

Makes admin UI feel like professional B2B tool at 100% zoom

src/components/admin/AdminSidebar.tsx

@@ -316,7 +316,7 @@ export default function AdminSidebar({ userRole }: SidebarProps) {
         ref={sidebarRef}
         id="admin-sidebar"
         className={[
-          "fixed top-0 left-0 h-full w-60 z-50",
+          "fixed top-0 left-0 h-full w-56 z-50",
           "border-r flex flex-col",
           "transition-transform duration-300 ease-out lg:translate-x-0",
           mobileOpen ? "translate-x-0" : "-translate-x-full",
@@ -408,7 +408,7 @@ export default function AdminSidebar({ userRole }: SidebarProps) {
                     onClick={() => closeMobileMenu()}
                     onKeyDown={(e) => handleNavKeyDown(e, item.href!, navIndex)}
                     className={[
-                      "group flex items-center gap-3 px-3 py-2.5 rounded-xl text-sm font-medium transition-all duration-200",
+                      "group flex items-center gap-2.5 px-3 py-2 rounded-lg text-xs font-medium transition-all duration-200",
                       "focus:outline-none focus-visible:ring-2 focus-visible:ring-offset-2 focus-visible:ring-offset-[var(--admin-sidebar-bg)]",
                       active
                         ? "border-l-[3px]"