feat: add Letzshop vendor directory with sync and admin management

- Add LetzshopVendorCache model to store cached vendor data from Letzshop API
- Create LetzshopVendorSyncService for syncing vendor directory
- Add Celery task for background vendor sync
- Create admin page at /admin/letzshop/vendor-directory with:
  - Stats dashboard (total, claimed, unclaimed vendors)
  - Searchable/filterable vendor list
  - "Sync Now" button to trigger sync
  - Ability to create platform vendors from Letzshop cache
- Add API endpoints for vendor directory management
- Add Pydantic schemas for API responses

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

app/tasks/celery_tasks/letzshop.py

@@ -1,19 +1,22 @@
 # app/tasks/celery_tasks/letzshop.py
 """
-Celery tasks for Letzshop historical order imports.
+Celery tasks for Letzshop integration.
 
-Wraps the existing process_historical_import function for Celery execution.
+Includes:
+- Historical order imports
+- Vendor directory sync
 """
 
 import logging
 from datetime import UTC, datetime
-from typing import Callable
+from typing import Any, Callable
 
 from app.core.celery_config import celery_app
 from app.services.admin_notification_service import admin_notification_service
 from app.services.letzshop import LetzshopClientError
 from app.services.letzshop.credentials_service import LetzshopCredentialsService
 from app.services.letzshop.order_service import LetzshopOrderService
+from app.services.letzshop.vendor_sync_service import LetzshopVendorSyncService
 from app.tasks.celery_tasks.base import DatabaseTask
 from models.database.letzshop import LetzshopHistoricalImportJob
 
@@ -270,3 +273,78 @@ def process_historical_import(self, job_id: int, vendor_id: int):
 
             db.commit()
             raise  # Re-raise for Celery retry
+
+
+# =============================================================================
+# Vendor Directory Sync
+# =============================================================================
+
+
+@celery_app.task(
+    bind=True,
+    base=DatabaseTask,
+    name="app.tasks.celery_tasks.letzshop.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 should be scheduled to run periodically (e.g., daily)
+    via Celery beat.
+
+    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,
+                )
+                db.commit()
+
+            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)},
+            )
+            db.commit()
+            raise  # Re-raise for Celery retry