feat: derive POSTGRES_DB and Redis prefix from DEPLOY_STAGE for pipeline isolation

services/shared/redis_keys.py

@@ -1,7 +1,10 @@
 """Redis key conventions and queue abstractions."""
 
+import os
+
 # --- Key prefixes ---
-PREFIX = "stonks"
+_STAGE = os.getenv("DEPLOY_STAGE", "")
+PREFIX = f"stonks:{_STAGE}" if _STAGE else "stonks"
 
 # Distributed locks
 LOCK_PREFIX = f"{PREFIX}:lock"