feat: add database engine and session management

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

app/database.py

@@ -0,0 +1,60 @@
+"""Database engine and session management.
+
+Provides a SQLModel engine factory and a session dependency
+for use with FastAPI's dependency injection.
+"""
+
+from pathlib import Path
+from typing import Generator
+
+import structlog
+from sqlmodel import Session, create_engine
+
+logger = structlog.get_logger(__name__)
+
+
+def get_engine(database_url: str):
+    """Create a SQLAlchemy engine for the given database URL.
+
+    For SQLite, ensures the parent directory exists and sets
+    appropriate connection arguments.
+
+    Args:
+        database_url: SQLAlchemy-compatible connection string.
+
+    Returns:
+        A configured SQLAlchemy Engine.
+    """
+    connect_args = {}
+    if database_url.startswith("sqlite"):
+        # Ensure the data directory exists
+        db_path = database_url.replace("sqlite:///", "")
+        if db_path and db_path != ":memory:":
+            Path(db_path).parent.mkdir(parents=True, exist_ok=True)
+        connect_args = {"check_same_thread": False}
+
+    engine = create_engine(
+        database_url,
+        connect_args=connect_args,
+        echo=False,
+    )
+    logger.info("database_engine_created", url=database_url)
+    return engine
+
+
+def get_db_session(engine) -> Generator[Session, None, None]:
+    """Yield a SQLModel session for dependency injection.
+
+    Usage in FastAPI routes:
+        @router.get("/example")
+        def example(session: Session = Depends(get_db_session)):
+            ...
+
+    Args:
+        engine: The SQLAlchemy engine to bind the session to.
+
+    Yields:
+        A SQLModel Session that auto-closes after use.
+    """
+    with Session(engine) as session:
+        yield session