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/exceptions.py

@@ -0,0 +1,105 @@
+# app/modules/marketplace/exceptions.py
+"""
+Marketplace module exceptions.
+
+Custom exceptions for Letzshop integration, product import/export, and sync operations.
+"""
+
+from app.exceptions import BusinessLogicException, ResourceNotFoundException
+
+
+class MarketplaceException(BusinessLogicException):
+    """Base exception for marketplace module errors."""
+
+    pass
+
+
+class LetzshopClientError(MarketplaceException):
+    """Raised when Letzshop API call fails."""
+
+    def __init__(self, message: str, status_code: int | None = None, response: str | None = None):
+        super().__init__(message)
+        self.status_code = status_code
+        self.response = response
+
+
+class LetzshopAuthenticationError(LetzshopClientError):
+    """Raised when Letzshop authentication fails."""
+
+    def __init__(self, message: str = "Letzshop authentication failed"):
+        super().__init__(message, status_code=401)
+
+
+class LetzshopCredentialsNotFoundException(ResourceNotFoundException):
+    """Raised when Letzshop credentials not found for vendor."""
+
+    def __init__(self, vendor_id: int):
+        super().__init__("LetzshopCredentials", str(vendor_id))
+        self.vendor_id = vendor_id
+
+
+class ImportJobNotFoundException(ResourceNotFoundException):
+    """Raised when a marketplace import job is not found."""
+
+    def __init__(self, job_id: int):
+        super().__init__("MarketplaceImportJob", str(job_id))
+
+
+class HistoricalImportJobNotFoundException(ResourceNotFoundException):
+    """Raised when a historical import job is not found."""
+
+    def __init__(self, job_id: int):
+        super().__init__("LetzshopHistoricalImportJob", str(job_id))
+
+
+class VendorNotFoundException(ResourceNotFoundException):
+    """Raised when a vendor is not found."""
+
+    def __init__(self, vendor_id: int):
+        super().__init__("Vendor", str(vendor_id))
+
+
+class ProductNotFoundException(ResourceNotFoundException):
+    """Raised when a marketplace product is not found."""
+
+    def __init__(self, product_id: str | int):
+        super().__init__("MarketplaceProduct", str(product_id))
+
+
+class ImportValidationError(MarketplaceException):
+    """Raised when import data validation fails."""
+
+    def __init__(self, message: str, errors: list[dict] | None = None):
+        super().__init__(message)
+        self.errors = errors or []
+
+
+class ExportError(MarketplaceException):
+    """Raised when product export fails."""
+
+    def __init__(self, message: str, language: str | None = None):
+        super().__init__(message)
+        self.language = language
+
+
+class SyncError(MarketplaceException):
+    """Raised when vendor directory sync fails."""
+
+    def __init__(self, message: str, vendor_code: str | None = None):
+        super().__init__(message)
+        self.vendor_code = vendor_code
+
+
+__all__ = [
+    "MarketplaceException",
+    "LetzshopClientError",
+    "LetzshopAuthenticationError",
+    "LetzshopCredentialsNotFoundException",
+    "ImportJobNotFoundException",
+    "HistoricalImportJobNotFoundException",
+    "VendorNotFoundException",
+    "ProductNotFoundException",
+    "ImportValidationError",
+    "ExportError",
+    "SyncError",
+]