Standalone mode unauthenticated by default

[raballew]

Description

--passphrase defaults to None at python/packages/jumpstarter-cli/jumpstarter_cli/run.py:245. Combined with --tls-grpc-insecure and 0.0.0.0 default binding, standalone mode exposes an unauthenticated, unencrypted gRPC server.

The PassphraseInterceptor at python/packages/jumpstarter/jumpstarter/exporter/auth.py:17-34 exists and works correctly, but defaults to disabled.

No warning is emitted when passphrase is absent (the most dangerous config), but a warning is present when passphrase is used without TLS (less dangerous) (run.py:107).

This applies ONLY to standalone mode; K8s mode has mandatory, non-disableable authentication.

Suggested Fix

• Generate random passphrase when --passphrase not provided
• Require explicit --unsafe-no-auth to disable authentication
• Warn when no passphrase and no TLS