feat(local_backend): reservations, print analytics, workday summary, zone-PIN management

- New reservations module: model, schema, router (CRUD + status updates + upcoming alerts)
  and background task for auto-expiring stale reservations
- Reports: print_products, print_categories, print_tables analytics endpoints
  plus meta_products and business_day_summary for workday close/view flow
- printer_service: configurable font sizes/weights, donut/bar chart print layout helpers,
  analytics print blocks per printer
- tables/schemas: surfaced color, zone, and other new fields on Table, Product, User, Printer
- demo_seed.py for quick dev DB population; wipe_database.py utility

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

local_backend/schemas/product.py

@@ -257,6 +257,7 @@ class PreferenceSetOut(BaseModel):
 
 class ProductBase(BaseModel):
     name: str
+    description: Optional[str] = None
     category_id: Optional[int] = None
     base_price: float
     is_available: bool = True
@@ -269,7 +270,7 @@ class ProductBase(BaseModel):
     digital_name: Optional[str] = None
     digital_description: Optional[str] = None
     digital_price: Optional[float] = None
-    digital_discount: float = 0.0
+    digital_discount: Optional[float] = None
     digital_image_url: Optional[str] = None
 
 
@@ -282,6 +283,7 @@ class ProductCreate(ProductBase):
 
 class ProductUpdate(BaseModel):
     name: Optional[str] = None
+    description: Optional[str] = None
     category_id: Optional[int] = None
     base_price: Optional[float] = None
     is_available: Optional[bool] = None