chore: establish project baseline

central/app/db.py

@@ -0,0 +1,15 @@
+"""SQLAlchemy session setup for central PostgreSQL only."""
+from sqlalchemy import create_engine, text
+from sqlalchemy.orm import sessionmaker
+from .config import settings
+
+engine = create_engine(settings.database_url, pool_pre_ping=True)
+SessionLocal = sessionmaker(bind=engine, expire_on_commit=False)
+
+def database_is_available() -> bool:
+    try:
+        with engine.connect() as connection:
+            connection.execute(text("SELECT 1"))
+        return True
+    except Exception:
+        return False