Restyle the admin panel to match AtomCMS's Filament housekeeping look

The admin pages used bare inline-styled tables on the default page
background. Rebuilt the admin shell + added a scoped .admin CSS layer so
the whole panel matches the original AtomCMS Filament look:
- Dark #2d2d44 sidebar (the AtomCMS admin navbar colour) with the nav
  grouped into Overview / Content / Users & access / Economy / Radio /
  System (mirrors the Filament resource groups), an avatar + rank badge
  header, and amber active-link highlighting via a client AdminNavLink
  (usePathname).
- A topbar ("Housekeeping" + signed-in user) over a light content area.
- Carded tables (surface bg, rounded, shadow, tinted header, row hover)
  and a page-title treatment, applied globally so every admin page is
  styled without per-page edits.

Verified in a real authenticated admin session (production server,
amx_test): sidebar renders #2d2d44 sticky, active link amber on dark
text, /admin/users table carded with 7 real rows; dev server serves the
admin rules after a cache refresh. tsc 0, vitest 49/49, next build 0.

src/app/globals.css

@@ -379,3 +379,188 @@ td {
 .coin.diamonds {
   background: #4bc0d9;
 }
+
+/* ── Admin panel (Housekeeping) ─────────────────────────────────
+   Faithful to AtomCMS's Filament panel: dark #2d2d44 sidebar with
+   grouped nav + amber active state, a topbar, and a light content
+   area with carded tables. Scoped under .admin so it never leaks
+   into the public site. */
+.admin {
+  display: grid;
+  grid-template-columns: 232px minmax(0, 1fr);
+  gap: 1.25rem;
+  align-items: start;
+}
+@media (max-width: 860px) {
+  .admin {
+    grid-template-columns: 1fr;
+  }
+}
+
+.admin-sidebar {
+  position: sticky;
+  top: 1rem;
+  align-self: start;
+  background: #2d2d44;
+  color: #e7e9f3;
+  border-radius: 14px;
+  padding: 0.85rem 0.7rem;
+  box-shadow: var(--shadow-card);
+  max-height: calc(100vh - 2rem);
+  overflow-y: auto;
+}
+.admin-sidebar-head {
+  display: flex;
+  align-items: center;
+  gap: 0.6rem;
+  padding: 0.3rem 0.45rem 0.85rem;
+  border-bottom: 1px solid rgba(255, 255, 255, 0.09);
+  margin-bottom: 0.5rem;
+}
+.admin-avatar {
+  flex: none;
+  width: 38px;
+  height: 38px;
+  border-radius: 10px;
+  display: grid;
+  place-items: center;
+  font-weight: 800;
+  color: #1a1a2e;
+  background: var(--color-primary, #eeb425);
+}
+.admin-sidebar-name {
+  font-weight: 700;
+  font-size: 0.92rem;
+  line-height: 1.1;
+  color: #fff;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+.admin-rank-badge {
+  display: inline-block;
+  margin-top: 0.2rem;
+  font-size: 0.66rem;
+  font-weight: 700;
+  text-transform: uppercase;
+  letter-spacing: 0.05em;
+  color: #1a1a2e;
+  background: var(--color-primary, #eeb425);
+  border-radius: 999px;
+  padding: 0.05rem 0.5rem;
+}
+.admin-nav {
+  display: flex;
+  flex-direction: column;
+  gap: 0.1rem;
+}
+.admin-nav-group {
+  margin-top: 0.55rem;
+}
+.admin-nav-group-label {
+  display: block;
+  font-size: 0.64rem;
+  font-weight: 700;
+  text-transform: uppercase;
+  letter-spacing: 0.09em;
+  color: rgba(231, 233, 243, 0.42);
+  padding: 0.3rem 0.55rem 0.25rem;
+}
+.admin-nav-link {
+  display: flex;
+  align-items: center;
+  gap: 0.55rem;
+  padding: 0.43rem 0.6rem;
+  border-radius: 9px;
+  color: #c8cbe0;
+  font-size: 0.85rem;
+  font-weight: 600;
+  text-decoration: none;
+  transition: background 0.15s ease, color 0.15s ease;
+}
+.admin-nav-link:hover {
+  background: rgba(255, 255, 255, 0.07);
+  color: #fff;
+  text-decoration: none;
+}
+.admin-nav-link.active {
+  background: var(--color-primary, #eeb425);
+  color: #1a1a2e;
+  box-shadow: 0 2px 8px rgba(238, 180, 37, 0.35);
+}
+
+.admin-content {
+  min-width: 0;
+}
+.admin-topbar {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 1rem;
+  background: var(--color-surface);
+  border: 1px solid var(--border);
+  border-radius: 12px;
+  padding: 0.7rem 1.15rem;
+  margin-bottom: 1.1rem;
+  box-shadow: var(--shadow-card);
+}
+.admin-topbar h2 {
+  margin: 0;
+  font-size: 1.05rem;
+  font-weight: 800;
+}
+
+/* Page content inside the admin panel */
+.admin-page main > h1:first-child,
+.admin-page > h1:first-child {
+  margin-top: 0;
+}
+.admin-page h1 {
+  font-size: 1.5rem;
+  padding-bottom: 0.5rem;
+  border-bottom: 2px solid var(--border);
+  margin-bottom: 0.85rem;
+}
+/* Carded tables — give the bare admin tables a surface + frame. */
+.admin-page table {
+  background: var(--color-surface);
+  box-shadow: var(--shadow-card);
+  border: 1px solid var(--border);
+  border-radius: 12px;
+  overflow: hidden;
+}
+.admin-page thead th {
+  background: color-mix(in srgb, var(--color-primary) 12%, var(--color-surface));
+  color: var(--color-text-muted);
+  border-bottom: 1px solid var(--border);
+  white-space: nowrap;
+}
+.admin-page th,
+.admin-page td {
+  padding: 0.6rem 0.8rem;
+}
+.admin-page tbody tr {
+  transition: background 0.12s ease;
+}
+.admin-page tbody tr:hover {
+  background: color-mix(in srgb, var(--color-primary) 7%, transparent);
+}
+.admin-page tbody td {
+  border-top: 1px solid color-mix(in srgb, var(--color-text-muted) 12%, transparent);
+}
+/* status pill used by some admin lists */
+.admin-badge {
+  display: inline-block;
+  font-size: 0.72rem;
+  font-weight: 700;
+  padding: 0.1rem 0.55rem;
+  border-radius: 999px;
+  background: color-mix(in srgb, var(--color-primary) 18%, transparent);
+  color: var(--color-text);
+}
+.admin-badge.ok {
+  background: color-mix(in srgb, #16a34a 20%, transparent);
+}
+.admin-badge.danger {
+  background: color-mix(in srgb, #ef4444 22%, transparent);
+}