Add export buttons to all admin panel screens

Backend export endpoints return DB data in seed JSON format
(games, routes+encounters, pokemon, evolutions). Frontend
downloads the JSON via new Export buttons on each admin page.

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

frontend/src/utils/download.ts

@@ -0,0 +1,11 @@
+export function downloadJson(data: unknown, filename: string) {
+  const blob = new Blob([JSON.stringify(data, null, 2)], { type: 'application/json' })
+  const url = URL.createObjectURL(blob)
+  const a = document.createElement('a')
+  a.href = url
+  a.download = filename
+  document.body.appendChild(a)
+  a.click()
+  document.body.removeChild(a)
+  URL.revokeObjectURL(url)
+}