perf(export): run export cores on the blocking pool

src-tauri/src/commands/database_export.rs

@@ -34,7 +34,9 @@ pub async fn export_database_sql(
     let state = state.inner().clone();
     let export_id = request.export_id.clone();
 
-    tokio::spawn(async move {
+    // Exports interleave async fetches with synchronous row formatting and
+    // buffered disk writes; run them off the async workers (see spawn_export_task).
+    dbx_core::export_runtime::spawn_export_task(async move {
         let result = dbx_core::database_export::export_database_sql_core(&state, &request, |progress| {
             emit_progress(&app, progress)
         })

src-tauri/src/commands/query_result_export.rs

@@ -269,7 +269,9 @@ pub async fn start_query_result_export(
     let target = StagedExportTarget::new(&request.file_path)?;
     request.file_path = target.path_string()?;
 
-    tokio::spawn(async move {
+    // Exports interleave async fetches with synchronous row formatting and
+    // buffered disk writes; run them off the async workers (see spawn_export_task).
+    dbx_core::export_runtime::spawn_export_task(async move {
         let execution_id = request.execution_id.clone().filter(|id| !id.trim().is_empty());
         let registered_query = execution_id.as_ref().map(|id| {
             state.running_queries.register_task(

src-tauri/src/commands/table_export.rs

@@ -29,7 +29,9 @@ pub async fn start_table_export(
     let export_id = request.export_id.clone();
     let file_path = request.file_path.clone();
 
-    tokio::spawn(async move {
+    // Exports interleave async fetches with synchronous row formatting and
+    // buffered disk writes; run them off the async workers (see spawn_export_task).
+    dbx_core::export_runtime::spawn_export_task(async move {
         let cancelled = Arc::new(AtomicBool::new(false));
         let cancelled_progress = cancelled.clone();
         let result = dbx_core::table_export::export_table_data_core(&state, &request, |progress| {