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/shift.py

@@ -0,0 +1,36 @@
+from sqlalchemy import Column, Integer, Float, 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 WaiterShift(Base):
+    __tablename__ = "waiter_shifts"
+
+    id = Column(Integer, primary_key=True, index=True)
+    waiter_id = Column(Integer, ForeignKey("users.id"), nullable=False)
+    business_day_id = Column(Integer, ForeignKey("business_days.id"), nullable=False)
+    started_at = Column(DateTime(timezone=True), default=_utcnow, nullable=False)
+    ended_at = Column(DateTime(timezone=True), nullable=True)
+    starting_cash = Column(Float, nullable=True)
+    total_collected = Column(Float, nullable=True)  # snapshot written at shift end
+    notes = Column(Text, nullable=True)
+
+    waiter = relationship("User", foreign_keys=[waiter_id])
+    business_day = relationship("BusinessDay", back_populates="shifts")
+    breaks = relationship("ShiftBreak", back_populates="shift", cascade="all, delete-orphan")
+
+
+class ShiftBreak(Base):
+    __tablename__ = "shift_breaks"
+
+    id = Column(Integer, primary_key=True, index=True)
+    shift_id = Column(Integer, ForeignKey("waiter_shifts.id"), nullable=False)
+    started_at = Column(DateTime(timezone=True), default=_utcnow, nullable=False)
+    ended_at = Column(DateTime(timezone=True), nullable=True)
+
+    shift = relationship("WaiterShift", back_populates="breaks")