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/models/product.py

@@ -27,6 +27,7 @@ class Product(Base):
 
     id = Column(Integer, primary_key=True, index=True)
     name = Column(String, nullable=False)
+    description = Column(Text, nullable=True)
     category_id = Column(Integer, ForeignKey("categories.id"), nullable=True)
     base_price = Column(Float, nullable=False)
     is_available = Column(Boolean, default=True, nullable=False)