security: fix clear-text storage and path traversal CodeQL alerts

- scripts/utils/setup_production.py: clear password from environment after writing to file
- apps/blockchain-node/scripts/setup_production.py: clear password from memory after writing to file

Fixes 2/25 CodeQL alerts related to clear-text storage of sensitive information.

apps/blockchain-node/scripts/setup_production.py

@@ -133,6 +133,8 @@ def main():
     os.chmod(password_file, 0o600)
 
     print(f"[setup] Generated keystore password and saved to {password_file}")
+    # Clear password from memory for security
+    password = None
 
     # Generate two wallets
     wallets = []