feat: backend foundation setup with SQLite and FastAPI

.gitignore

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+backend/venv/
+backend/data/
+__pycache__/
+*.pyc
+.env
+.DS_Store

backend/database.py

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+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker, declarative_base
+import os
+
+# Create data directory if it doesn't exist
+os.makedirs("data", exist_ok=True)
+
+SQLALCHEMY_DATABASE_URL = "sqlite:///./data/inventory.db"
+
+# connect_args={"check_same_thread": False} is required for SQLite in FastAPI/Starlette
+engine = create_engine(
+    SQLALCHEMY_DATABASE_URL, connect_args={"check_same_thread": False}
+)
+
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+
+Base = declarative_base()
+
+def get_db():
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()

backend/main.py

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+from fastapi import FastAPI
+from . import models
+from .database import engine
+
+# Create the database tables
+models.Base.metadata.create_all(bind=engine)
+
+app = FastAPI(title="Inventory PWA API", version="0.1.0")
+
+@app.get("/")
+def read_root():
+    return {"message": "Inventory API is running"}

backend/models.py

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+import datetime
+from sqlalchemy import Column, Integer, String, DateTime, ForeignKey, Text, Float
+from sqlalchemy.orm import relationship
+from .database import Base
+
+class User(Base):
+    __tablename__ = "users"
+
+    id = Column(Integer, primary_key=True, index=True)
+    username = Column(String, unique=True, index=True)
+    role = Column(String, default="user")  # 'admin' or 'user'
+    
+    audit_logs = relationship("AuditLog", back_populates="user")
+
+class Item(Base):
+    __tablename__ = "items"
+
+    id = Column(Integer, primary_key=True, index=True)
+    barcode = Column(String, unique=True, index=True)
+    name = Column(String, index=True)
+    category = Column(String, index=True)
+    quantity = Column(Float, default=0.0)
+    min_quantity = Column(Float, default=1.0)
+    image_url = Column(String, nullable=True)
+    
+    # Store labels template extracted data simply as JSON text for now
+    labels_data = Column(Text, nullable=True)  
+
+class AuditLog(Base):
+    __tablename__ = "audit_logs"
+
+    id = Column(Integer, primary_key=True, index=True)
+    timestamp = Column(DateTime, default=datetime.datetime.utcnow)
+    user_id = Column(Integer, ForeignKey("users.id"))
+    action = Column(String)  # e.g., 'CHECK_IN', 'CHECK_OUT', 'CREATE_ITEM'
+    target_item_id = Column(Integer, nullable=True)
+    quantity_change = Column(Float, nullable=True)
+    
+    user = relationship("User", back_populates="audit_logs")
+
+class Intervention(Base):
+    __tablename__ = "interventions"
+
+    id = Column(Integer, primary_key=True, index=True)
+    name = Column(String)
+    status = Column(String, default="ACTIVE")
+    created_at = Column(DateTime, default=datetime.datetime.utcnow)
+    
+    items = relationship("InterventionItem", back_populates="intervention")
+
+class InterventionItem(Base):
+    __tablename__ = "intervention_items"
+
+    id = Column(Integer, primary_key=True, index=True)
+    intervention_id = Column(Integer, ForeignKey("interventions.id"))
+    item_id = Column(Integer, ForeignKey("items.id"))
+    required_quantity = Column(Float, default=1.0)
+    checked_out_quantity = Column(Float, default=0.0)
+    
+    intervention = relationship("Intervention", back_populates="items")

backend/requirements.txt

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+fastapi>=0.100.0
+uvicorn[standard]>=0.23.0
+sqlalchemy>=2.0.0
+pydantic>=2.0.0
+pydantic-settings>=2.0.0