feat: migrate persistence from JSON to SQLModel (Phase 1)

- Integrated SQLModel with SQLite for robust data persistence
- Refactored UserManager and WatchlistManager to use SQL queries
- Migrated models to SQLModel with relationships and primary keys
- Updated test suite with in-memory database isolation
- Removed deprecated JSON storage files

app/database.py

@@ -0,0 +1,31 @@
+"""Database configuration and session management using SQLModel"""
+import os
+from typing import Generator
+from sqlalchemy import create_engine
+from sqlmodel import SQLModel, Session, create_engine
+from app.config import get_settings
+
+settings = get_settings()
+
+# Database URL can be overridden by environment variable DATABASE_URL
+DATABASE_URL = os.getenv("DATABASE_URL", "sqlite:///./ohm_streaming.db")
+
+# Create the engine
+# connect_args={"check_same_thread": False} is required for SQLite and FastAPI
+engine = create_engine(DATABASE_URL, connect_args={"check_same_thread": False})
+
+
+def create_db_and_tables():
+    """Create the database and tables based on the models"""
+    # Import all models here to ensure they are registered with SQLModel.metadata
+    from app.models.auth import UserTable
+    from app.models.watchlist import WatchlistItemTable
+    # Add other models as they are migrated
+    
+    SQLModel.metadata.create_all(engine)
+
+
+def get_session() -> Generator[Session, None, None]:
+    """Dependency for getting a database session"""
+    with Session(engine) as session:
+        yield session