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>

models/schema/letzshop.py

@@ -507,3 +507,120 @@ class LetzshopHistoricalImportStartResponse(BaseModel):
     job_id: int
     status: str = "pending"
     message: str = "Historical import job started"
+
+
+# ============================================================================
+# Vendor Directory Schemas (Letzshop Marketplace Cache)
+# ============================================================================
+
+
+class LetzshopCachedVendorItem(BaseModel):
+    """Schema for a cached Letzshop vendor in list view."""
+
+    id: int
+    letzshop_id: str
+    slug: str
+    name: str
+    company_name: str | None = None
+    email: str | None = None
+    phone: str | None = None
+    website: str | None = None
+    city: str | None = None
+    categories: list[str] = []
+    is_active: bool = True
+    is_claimed: bool = False
+    claimed_by_vendor_id: int | None = None
+    last_synced_at: datetime | None = None
+    letzshop_url: str
+
+
+class LetzshopCachedVendorDetail(BaseModel):
+    """Schema for detailed cached Letzshop vendor."""
+
+    id: int
+    letzshop_id: str
+    slug: str
+    name: str
+    company_name: str | None = None
+    description_en: str | None = None
+    description_fr: str | None = None
+    description_de: str | None = None
+    email: str | None = None
+    phone: str | None = None
+    fax: str | None = None
+    website: str | None = None
+    street: str | None = None
+    street_number: str | None = None
+    city: str | None = None
+    zipcode: str | None = None
+    country_iso: str | None = None
+    latitude: str | None = None
+    longitude: str | None = None
+    categories: list[str] = []
+    background_image_url: str | None = None
+    social_media_links: list[str] = []
+    opening_hours_en: str | None = None
+    opening_hours_fr: str | None = None
+    opening_hours_de: str | None = None
+    representative_name: str | None = None
+    representative_title: str | None = None
+    is_active: bool = True
+    is_claimed: bool = False
+    claimed_by_vendor_id: int | None = None
+    claimed_at: datetime | None = None
+    last_synced_at: datetime | None = None
+    letzshop_url: str
+
+
+class LetzshopVendorDirectoryStats(BaseModel):
+    """Schema for vendor directory cache statistics."""
+
+    total_vendors: int = 0
+    active_vendors: int = 0
+    claimed_vendors: int = 0
+    unclaimed_vendors: int = 0
+    unique_cities: int = 0
+    last_synced_at: str | None = None
+
+
+class LetzshopVendorDirectoryStatsResponse(BaseModel):
+    """Response schema for vendor directory stats endpoint."""
+
+    success: bool = True
+    stats: LetzshopVendorDirectoryStats
+
+
+class LetzshopCachedVendorListResponse(BaseModel):
+    """Response schema for vendor directory list endpoint."""
+
+    success: bool = True
+    vendors: list[LetzshopCachedVendorItem]
+    total: int
+    page: int
+    limit: int
+    has_more: bool
+
+
+class LetzshopCachedVendorDetailResponse(BaseModel):
+    """Response schema for vendor directory detail endpoint."""
+
+    success: bool = True
+    vendor: LetzshopCachedVendorDetail
+
+
+class LetzshopVendorDirectorySyncResponse(BaseModel):
+    """Response schema for vendor directory sync trigger."""
+
+    success: bool = True
+    message: str
+    task_id: str | None = None
+    mode: str = "celery"
+
+
+class LetzshopCreateVendorFromCacheResponse(BaseModel):
+    """Response schema for creating vendor from Letzshop cache."""
+
+    success: bool = True
+    message: str
+    vendor: dict[str, Any] | None = None
+    letzshop_vendor_slug: str