feat(admin): transfer user accounts and show local cover coverage

apps/web/src/features/users/transfer.ts

@@ -0,0 +1,29 @@
+import type { components } from '@pipu/api-client';
+
+export type UserArchive = components['schemas']['UserArchive'];
+export const MAX_ARCHIVE_BYTES = 16 * 1024 * 1024;
+
+/** Only previews metadata; the server validates every account before writing. */
+export function parseUserArchive(text: string): UserArchive {
+  const data: unknown = JSON.parse(text.replace(/^\uFEFF/, ''));
+  if (!data || typeof data !== 'object' || !('version' in data) || data.version !== 1 ||
+      !('users' in data) || !Array.isArray(data.users) || data.users.length > 10000) throw new Error('archive');
+  for (const entry of data.users) {
+    if (!entry || typeof entry !== 'object' || typeof entry.username !== 'string' ||
+        !['admin', 'moderator', 'user'].includes(entry.role) || typeof entry.password_hash !== 'string') {
+      throw new Error('archive');
+    }
+  }
+  return data as UserArchive;
+}
+
+export function downloadUserArchive(archive: UserArchive) {
+  const url = URL.createObjectURL(new Blob([JSON.stringify(archive, null, 2)], { type: 'application/json' }));
+  const link = document.createElement('a');
+  link.href = url;
+  link.download = 'pipu-users.json';
+  document.body.append(link);
+  link.click();
+  link.remove();
+  setTimeout(() => URL.revokeObjectURL(url), 1000);
+}