refactor: move LetzshopExportRequest to schema layer

Follows architecture rule: Pydantic schemas belong in models/schema/

- Moved LetzshopExportRequest to models/schema/vendor.py
- Added LetzshopExportFileInfo and LetzshopExportResponse schemas
- Updated API endpoint to use proper response_model
- Removed inline BaseModel import from API file

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/api/v1/admin/vendors.py

@@ -11,7 +11,6 @@ Architecture Notes:
 import logging
 
 from fastapi import APIRouter, Body, Depends, Path, Query
-from pydantic import BaseModel
 from sqlalchemy.orm import Session
 
 from app.api.deps import get_current_admin_api
@@ -23,6 +22,8 @@ from app.services.vendor_service import vendor_service
 from models.database.user import User
 from models.schema.stats import VendorStatsResponse
 from models.schema.vendor import (
+    LetzshopExportRequest,
+    LetzshopExportResponse,
     VendorCreate,
     VendorCreateResponse,
     VendorDetailResponse,
@@ -366,13 +367,7 @@ def export_vendor_products_letzshop(
     )
 
 
-class LetzshopExportRequest(BaseModel):
-    """Request body for Letzshop export to pickup folder."""
-
-    include_inactive: bool = False
-
-
-@router.post("/{vendor_identifier}/export/letzshop")
+@router.post("/{vendor_identifier}/export/letzshop", response_model=LetzshopExportResponse)
 def export_vendor_products_letzshop_to_folder(
     vendor_identifier: str = Path(..., description="Vendor ID or vendor_code"),
     request: LetzshopExportRequest = None,