feat: complete unified order model integration for Letzshop API

Update API endpoints and schemas to use the unified Order model:
- Update Letzshop order schemas with OrderItem support
- Update API responses to use new field names (external_*, status, etc.)
- Update confirm/reject endpoints to use OrderItem.external_item_id
- Update Letzshop order service for unified Order model queries
- Update documentation to reflect completed implementation

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

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

models/schema/letzshop.py

@@ -71,76 +71,119 @@ class LetzshopCredentialsStatus(BaseModel):
 
 
 # ============================================================================
-# Letzshop Order Schemas
+# Letzshop Order Schemas (using unified Order model)
 # ============================================================================
 
 
-class LetzshopInventoryUnit(BaseModel):
-    """Schema for Letzshop inventory unit."""
+class LetzshopOrderItemResponse(BaseModel):
+    """Schema for order item in Letzshop order response."""
 
-    id: str
-    state: str
+    model_config = ConfigDict(from_attributes=True)
+
+    id: int
+    product_id: int
+    product_name: str
+    product_sku: str | None = None
+    gtin: str | None = None
+    gtin_type: str | None = None
+    quantity: int
+    unit_price: float
+    total_price: float
+    external_item_id: str | None = None  # Letzshop inventory unit ID
+    external_variant_id: str | None = None
+    item_state: str | None = None  # confirmed_available, confirmed_unavailable
 
 
-class LetzshopOrderBase(BaseModel):
-    """Base schema for Letzshop order."""
-
-    letzshop_order_id: str
-    letzshop_shipment_id: str | None = None
-    letzshop_order_number: str | None = None
-    letzshop_state: str | None = None
-    customer_email: str | None = None
-    customer_name: str | None = None
-    customer_locale: str | None = None
-    shipping_country_iso: str | None = None
-    billing_country_iso: str | None = None
-    total_amount: str | None = None
-    currency: str = "EUR"
-
-
-class LetzshopOrderCreate(LetzshopOrderBase):
-    """Schema for creating a Letzshop order record."""
-
-    vendor_id: int
-    raw_order_data: dict[str, Any] | None = None
-    inventory_units: list[dict[str, Any]] | None = None
-
-
-class LetzshopOrderResponse(LetzshopOrderBase):
-    """Schema for Letzshop order response."""
+class LetzshopOrderResponse(BaseModel):
+    """Schema for Letzshop order response (from unified Order model)."""
 
     model_config = ConfigDict(from_attributes=True)
 
     id: int
     vendor_id: int
-    local_order_id: int | None
-    sync_status: str
-    last_synced_at: datetime | None
-    sync_error: str | None
-    confirmed_at: datetime | None
-    rejected_at: datetime | None
-    tracking_set_at: datetime | None
-    tracking_number: str | None
-    tracking_carrier: str | None
-    inventory_units: list[dict[str, Any]] | None
-    order_date: datetime | None
+    order_number: str
+
+    # External references
+    external_order_id: str | None = None
+    external_shipment_id: str | None = None
+    external_order_number: str | None = None
+
+    # Status
+    status: str  # pending, processing, shipped, delivered, cancelled
+
+    # Customer info
+    customer_email: str
+    customer_name: str  # computed: customer_first_name + customer_last_name
+    customer_locale: str | None = None
+
+    # Address info
+    ship_country_iso: str
+    bill_country_iso: str
+
+    # Financial
+    total_amount: float
+    currency: str = "EUR"
+
+    # Tracking
+    tracking_number: str | None = None
+    tracking_provider: str | None = None
+
+    # Timestamps
+    order_date: datetime
+    confirmed_at: datetime | None = None
+    shipped_at: datetime | None = None
+    cancelled_at: datetime | None = None
     created_at: datetime
     updated_at: datetime
 
+    # Items (for list view, may be empty)
+    items: list[LetzshopOrderItemResponse] = Field(default_factory=list)
+
 
 class LetzshopOrderDetailResponse(LetzshopOrderResponse):
-    """Schema for detailed Letzshop order response with raw data."""
+    """Schema for detailed Letzshop order response with all data."""
 
-    raw_order_data: dict[str, Any] | None = None
+    # Full customer snapshot
+    customer_first_name: str
+    customer_last_name: str
+    customer_phone: str | None = None
+
+    # Full shipping address
+    ship_first_name: str
+    ship_last_name: str
+    ship_company: str | None = None
+    ship_address_line_1: str
+    ship_address_line_2: str | None = None
+    ship_city: str
+    ship_postal_code: str
+
+    # Full billing address
+    bill_first_name: str
+    bill_last_name: str
+    bill_company: str | None = None
+    bill_address_line_1: str
+    bill_address_line_2: str | None = None
+    bill_city: str
+    bill_postal_code: str
+
+    # Raw marketplace data
+    external_data: dict[str, Any] | None = None
+
+    # Notes
+    customer_notes: str | None = None
+    internal_notes: str | None = None
 
 
 class LetzshopOrderStats(BaseModel):
     """Schema for order statistics by status."""
 
     pending: int = 0
-    confirmed: int = 0
-    rejected: int = 0
+    processing: int = 0
     shipped: int = 0
+    delivered: int = 0
+    cancelled: int = 0
+    total: int = 0
+    has_declined_items: int = 0  # Orders with at least one declined item
 
 
 class LetzshopOrderListResponse(BaseModel):
@@ -150,7 +193,7 @@ class LetzshopOrderListResponse(BaseModel):
     total: int
     skip: int
     limit: int
-    stats: LetzshopOrderStats | None = None  # Order counts by sync_status
+    stats: LetzshopOrderStats | None = None
 
 
 # ============================================================================
@@ -191,7 +234,7 @@ class FulfillmentQueueItemResponse(BaseModel):
 
     id: int
     vendor_id: int
-    letzshop_order_id: int
+    order_id: int  # FK to unified orders table
     operation: str
     payload: dict[str, Any]
     status: str