Add Polaris FastAPI backend: models/schemas, pricing+scoring+order router, importer, Celery tasks, API routers, seed script

backend/app/database.py

@@ -0,0 +1,30 @@
+"""Database engine/session wiring.
+
+DATABASE_URL comes from env (set by docker-compose). On the CT host it falls
+back to the local postgres port mapping using POSTGRES_PASSWORD from .env.
+"""
+import os
+
+from dotenv import load_dotenv
+from sqlalchemy import create_engine
+from sqlalchemy.orm import declarative_base, sessionmaker
+
+# /opt/polaris/.env exists on the CT host; harmless no-op elsewhere.
+load_dotenv(os.getenv("POLARIS_ENV_FILE", "/opt/polaris/.env"), override=False)
+
+DATABASE_URL = os.getenv(
+    "DATABASE_URL",
+    f"postgresql+psycopg2://reseller:{os.getenv('POSTGRES_PASSWORD', '')}@127.0.0.1:5432/reseller",
+)
+
+engine = create_engine(DATABASE_URL, pool_pre_ping=True, pool_size=5, max_overflow=10)
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+Base = declarative_base()
+
+
+def get_db():
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()