feat: initial commit — local services (backend + manager dashboard + waiter PWA)

Includes all work to date:
- local_backend: FastAPI backend with products, orders, tables, shifts, cloud sync
- manager_dashboard: React manager UI with product/category management, reports, settings
- waiter_pwa: React PWA for waiter devices
- Category reparent endpoint and UI
- Waiter domain: local_ip sent on heartbeat, waiter_domain persisted from cloud response
- QR code modal in AppInfoTab for waiter domain
- Product form: number input spinners removed, category pre-selected on new product
- Category row: count badge moved to far right

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

local_backend/models/business_day.py

@@ -0,0 +1,24 @@
+from sqlalchemy import Column, Integer, String, DateTime, ForeignKey, Text
+from sqlalchemy.orm import relationship
+from datetime import datetime, timezone
+from database import Base
+
+
+def _utcnow():
+    return datetime.now(timezone.utc)
+
+
+class BusinessDay(Base):
+    __tablename__ = "business_days"
+
+    id = Column(Integer, primary_key=True, index=True)
+    status = Column(String, default="open", nullable=False)  # 'open' | 'closed'
+    opened_at = Column(DateTime(timezone=True), default=_utcnow, nullable=False)
+    opened_by_id = Column(Integer, ForeignKey("users.id"), nullable=False)
+    closed_at = Column(DateTime(timezone=True), nullable=True)
+    closed_by_id = Column(Integer, ForeignKey("users.id"), nullable=True)
+    notes = Column(Text, nullable=True)
+
+    opener = relationship("User", foreign_keys=[opened_by_id])
+    closer = relationship("User", foreign_keys=[closed_by_id])
+    shifts = relationship("WaiterShift", back_populates="business_day")