feat: complete marketplace module migration (Phase 6)

Migrates marketplace module to self-contained structure:
- Create app/modules/marketplace/services/ re-exporting from existing locations
- Create app/modules/marketplace/models/ with marketplace & letzshop models
- Create app/modules/marketplace/schemas/ with product & import schemas
- Create app/modules/marketplace/tasks/ with 5 Celery tasks:
  - process_marketplace_import - CSV product import
  - process_historical_import - Letzshop order import
  - sync_vendor_directory - Scheduled daily vendor sync
  - export_vendor_products_to_folder - Multi-language export
  - export_marketplace_products - Admin export
- Create app/modules/marketplace/exceptions.py
- Update definition.py with is_self_contained=True and scheduled_tasks

Celery task migration:
- process_marketplace_import, process_historical_import -> import_tasks.py
- sync_vendor_directory -> sync_tasks.py (scheduled daily at 02:00)
- export_vendor_products_to_folder, export_marketplace_products -> export_tasks.py

Backward compatibility:
- Legacy task files now re-export from new locations
- Remove marketplace/letzshop/export from LEGACY_TASK_MODULES

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/modules/marketplace/tasks/sync_tasks.py

@@ -0,0 +1,84 @@
+# app/modules/marketplace/tasks/sync_tasks.py
+"""
+Celery tasks for Letzshop vendor directory synchronization.
+
+Periodically syncs vendor information from Letzshop's public GraphQL API.
+"""
+
+import logging
+from typing import Any
+
+from app.core.celery_config import celery_app
+from app.modules.task_base import ModuleTask
+from app.services.admin_notification_service import admin_notification_service
+from app.services.letzshop.vendor_sync_service import LetzshopVendorSyncService
+
+logger = logging.getLogger(__name__)
+
+
+@celery_app.task(
+    bind=True,
+    base=ModuleTask,
+    name="app.modules.marketplace.tasks.sync_tasks.sync_vendor_directory",
+    max_retries=2,
+    default_retry_delay=300,
+    autoretry_for=(Exception,),
+    retry_backoff=True,
+)
+def sync_vendor_directory(self) -> dict[str, Any]:
+    """
+    Celery task to sync Letzshop vendor directory.
+
+    Fetches all vendors from Letzshop's public GraphQL API and updates
+    the local letzshop_vendor_cache table.
+
+    This task is scheduled to run daily via the module's scheduled_tasks
+    definition.
+
+    Returns:
+        dict: Sync statistics including created, updated, and error counts.
+    """
+    with self.get_db() as db:
+        try:
+            logger.info("Starting Letzshop vendor directory sync...")
+
+            sync_service = LetzshopVendorSyncService(db)
+
+            def progress_callback(page: int, fetched: int, total: int):
+                """Log progress during sync."""
+                logger.info(f"Vendor sync progress: page {page}, {fetched}/{total} vendors")
+
+            stats = sync_service.sync_all_vendors(progress_callback=progress_callback)
+
+            logger.info(
+                f"Vendor directory sync completed: "
+                f"{stats.get('created', 0)} created, "
+                f"{stats.get('updated', 0)} updated, "
+                f"{stats.get('errors', 0)} errors"
+            )
+
+            # Send admin notification if there were errors
+            if stats.get("errors", 0) > 0:
+                admin_notification_service.notify_system_info(
+                    db=db,
+                    title="Letzshop Vendor Sync Completed with Errors",
+                    message=(
+                        f"Synced {stats.get('total_fetched', 0)} vendors. "
+                        f"Errors: {stats.get('errors', 0)}"
+                    ),
+                    details=stats,
+                )
+
+            return stats
+
+        except Exception as e:
+            logger.error(f"Vendor directory sync failed: {e}", exc_info=True)
+
+            # Notify admins of failure
+            admin_notification_service.notify_critical_error(
+                db=db,
+                error_type="Vendor Directory Sync",
+                error_message=f"Failed to sync Letzshop vendor directory: {str(e)[:200]}",
+                details={"error": str(e)},
+            )
+            raise  # Re-raise for Celery retry