feat: batches with dry run, undo, and CSV import and export

- POST /_seo/api/v1/batch runs changes in one transaction: dry_run
  answers the diff and the conflicts (loops, chains, noindex on a
  published record, canonicals to redirected or noindex addresses) and
  rolls back; a refused change refuses the batch (D-12)
- undo of a change or a whole batch from History and through MCP, with
  the undo_stale, undo_loop and undo_gone refusals (D-13)
- CSV export and import of redirects, rules and records by URL: BOM,
  comma or semicolon, formula cells escaped, a dry-run preview, all or
  nothing with via import; the screen's apply token is HMAC-SHA256 over
  the file and a fingerprint of the data (transfer.stale)
- Import and export singleton with the seo_transfer widget action,
  History record actions undo and undo_batch, navigation entry
- MCP tools undo_change, undo_batch, apply_batch, export_csv, import_csv
- TestBatch, TestUndo, TestCSVTransfer, TestLoopRefused mcp and import

controllers/admin_registry.go

@@ -34,6 +34,7 @@ func AdminControllers(app func() *backpack.App) []pact.AdminController {
 		rulesAdminController{app: app},
 		robotsAdminController{app: app},
 		historyAdminController{app: app},
+		transferAdminController{app: app},
 	}
 }