feat: Datenmodell (SQLAlchemy) und Alembic-Migration

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

finance/app/db.py

@@ -0,0 +1,23 @@
+from sqlalchemy import create_engine
+from sqlalchemy.orm import DeclarativeBase, Session
+
+from app.config import get_settings
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+_engine = None
+
+
+def get_engine():
+    global _engine
+    if _engine is None:
+        _engine = create_engine(get_settings().database_url)
+    return _engine
+
+
+def get_session():
+    with Session(get_engine()) as session:
+        yield session