feat: add admin panel with Discord OAuth and dashboard

Adds a React admin panel (panel/) with Discord OAuth2 login,
live dashboard via WebSocket, and settings/management pages.
Includes Docker build support, Vite proxy config for dev,
game_settings migration, and open-redirect protection on auth callback.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

panel/src/components/DataTable.tsx

@@ -0,0 +1,73 @@
+import type { ReactNode } from "react";
+
+export interface Column<T> {
+  key: string;
+  header: string;
+  render?: (row: T) => ReactNode;
+  className?: string;
+}
+
+interface DataTableProps<T> {
+  columns: Column<T>[];
+  data: T[];
+  keyField: string;
+  loading?: boolean;
+  onRowClick?: (row: T) => void;
+  emptyMessage?: string;
+}
+
+export default function DataTable<T extends Record<string, unknown>>({
+  columns,
+  data,
+  keyField,
+  loading,
+  onRowClick,
+  emptyMessage = "No data found",
+}: DataTableProps<T>) {
+  if (loading) {
+    return (
+      <div className="flex justify-center p-8">
+        <span className="loading loading-spinner loading-lg" />
+      </div>
+    );
+  }
+
+  return (
+    <div className="overflow-x-auto">
+      <table className="table table-zebra w-full">
+        <thead>
+          <tr>
+            {columns.map((col) => (
+              <th key={col.key} className={col.className}>
+                {col.header}
+              </th>
+            ))}
+          </tr>
+        </thead>
+        <tbody>
+          {data.length === 0 ? (
+            <tr>
+              <td colSpan={columns.length} className="text-center py-8 text-base-content/50">
+                {emptyMessage}
+              </td>
+            </tr>
+          ) : (
+            data.map((row) => (
+              <tr
+                key={String(row[keyField])}
+                className={onRowClick ? "cursor-pointer hover" : ""}
+                onClick={() => onRowClick?.(row)}
+              >
+                {columns.map((col) => (
+                  <td key={col.key} className={col.className}>
+                    {col.render ? col.render(row) : String(row[col.key] ?? "")}
+                  </td>
+                ))}
+              </tr>
+            ))
+          )}
+        </tbody>
+      </table>
+    </div>
+  );
+}