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/definition.py

@@ -3,12 +3,12 @@
 Marketplace module definition.
 
 Defines the marketplace module including its features, menu items,
-dependencies, and route configurations.
+dependencies, route configurations, and scheduled tasks.
 
 Note: This module requires the inventory module to be enabled.
 """
 
-from app.modules.base import ModuleDefinition
+from app.modules.base import ModuleDefinition, ScheduledTask
 from models.database.admin_menu_config import FrontendType
 
 
@@ -34,6 +34,7 @@ marketplace_module = ModuleDefinition(
         "Letzshop marketplace integration for product sync, order import, "
         "and catalog synchronization."
     ),
+    version="1.0.0",
     requires=["inventory"],  # Depends on inventory module
     features=[
         "letzshop_sync",  # Sync products with Letzshop
@@ -52,6 +53,26 @@ marketplace_module = ModuleDefinition(
         ],
     },
     is_core=False,
+    # =========================================================================
+    # Self-Contained Module Configuration
+    # =========================================================================
+    is_self_contained=True,
+    services_path="app.modules.marketplace.services",
+    models_path="app.modules.marketplace.models",
+    schemas_path="app.modules.marketplace.schemas",
+    exceptions_path="app.modules.marketplace.exceptions",
+    tasks_path="app.modules.marketplace.tasks",
+    # =========================================================================
+    # Scheduled Tasks
+    # =========================================================================
+    scheduled_tasks=[
+        ScheduledTask(
+            name="marketplace.sync_vendor_directory",
+            task="app.modules.marketplace.tasks.sync_tasks.sync_vendor_directory",
+            schedule="0 2 * * *",  # Daily at 02:00
+            options={"queue": "scheduled"},
+        ),
+    ],
 )