feat(mui): kit primitives — PageHeader, EmptyState, LoadingState, FilterBar, StatCard + DataTable onRowClick/rowDanger

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/ui/EmptyState.tsx

@@ -0,0 +1,52 @@
+import type { ReactNode } from "react";
+import Box from "@mui/material/Box";
+import Typography from "@mui/material/Typography";
+
+export interface EmptyStateProps {
+  icon?: ReactNode;
+  title: string;
+  description?: string;
+  action?: ReactNode;
+}
+
+/** Centered empty-state placeholder: icon, title, description, optional CTA. */
+export default function EmptyState({
+  icon,
+  title,
+  description,
+  action,
+}: EmptyStateProps) {
+  return (
+    <Box
+      sx={{
+        display: "flex",
+        flexDirection: "column",
+        alignItems: "center",
+        textAlign: "center",
+        py: 6,
+        color: "text.secondary",
+        gap: 1,
+      }}
+    >
+      {icon && (
+        <Box
+          sx={{ color: "text.disabled", mb: 0.5, fontSize: 48, lineHeight: 1 }}
+        >
+          {icon}
+        </Box>
+      )}
+      <Typography
+        variant="subtitle1"
+        sx={{ fontWeight: 500, color: "text.secondary" }}
+      >
+        {title}
+      </Typography>
+      {description && (
+        <Typography variant="body2" color="text.secondary">
+          {description}
+        </Typography>
+      )}
+      {action && <Box sx={{ mt: 1.5 }}>{action}</Box>}
+    </Box>
+  );
+}