Set up database configuration and connection management

- Created app/database.py with SQLAlchemy engine, session management, and connection utilities
- Added comprehensive database models in app/models.py for User, Client, Phone, Case, Transaction, Document, and Payment
- Implemented FastAPI application with database lifecycle management in app/main.py
- Added health check endpoint to verify database connectivity
- Created README.md with database configuration documentation
- Verified database connection works correctly with SQLite backend

app/database.py

@@ -0,0 +1,91 @@
+"""
+Database configuration and connection management for Delphi Database application.
+
+This module handles SQLAlchemy engine creation, session management, and provides
+database connection utilities for the FastAPI application.
+"""
+
+import os
+from typing import Generator
+
+from sqlalchemy import create_engine
+from sqlalchemy.ext.declarative import declarative_base
+from sqlalchemy.orm import sessionmaker, Session
+from dotenv import load_dotenv
+
+# Load environment variables from .env file
+load_dotenv()
+
+# Database configuration from environment variables
+DATABASE_URL = os.getenv(
+    "DATABASE_URL",
+    "sqlite:///./delphi.db"  # Default to SQLite for development
+)
+
+# Create SQLAlchemy engine
+engine = create_engine(
+    DATABASE_URL,
+    connect_args={"check_same_thread": False} if "sqlite" in DATABASE_URL else {},
+    pool_pre_ping=True,  # Verify connections before reuse
+    echo=False  # Set to True for SQL query logging in development
+)
+
+# Create session factory
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+
+# Create declarative base for models
+Base = declarative_base()
+
+
+def get_db() -> Generator[Session, None, None]:
+    """
+    Dependency function that provides a database session.
+
+    Yields a database session and ensures it's properly closed after use.
+    Used as a FastAPI dependency in route handlers.
+
+    Yields:
+        Session: SQLAlchemy database session
+
+    Example:
+        @app.get("/items/")
+        async def read_items(db: Session = Depends(get_db)):
+            return db.query(Item).all()
+    """
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()
+
+
+def create_tables() -> None:
+    """
+    Create all database tables defined in SQLAlchemy models.
+
+    This function should be called during application startup to ensure
+    all tables exist in the database.
+    """
+    Base.metadata.create_all(bind=engine)
+
+
+def get_database_url() -> str:
+    """
+    Get the current database URL (with sensitive info masked).
+
+    Returns:
+        str: Database URL with password masked for logging
+    """
+    if "sqlite" in DATABASE_URL:
+        return DATABASE_URL
+
+    # For PostgreSQL/MySQL, mask the password
+    if "@" in DATABASE_URL:
+        parts = DATABASE_URL.split("@")
+        if "://" in parts[0]:
+            protocol_and_auth = parts[0].split("://")[1]
+            if ":" in protocol_and_auth:
+                user_pass, host_port = protocol_and_auth.split(":", 1)
+                return DATABASE_URL.replace(user_pass, "****")
+
+    return "****://****:****@****/****"