Fix flux Dockerfile pip line and harden

[garland3]

Fix flux Dockerfile pip line and harden

Severity: Medium | Area: Containers | Labels: containers, hardening

Files

• docker/flux/Dockerfile

Summary

• Missing && before pip install flux-python; same hardening as other images.

Acceptance Criteria

• Ensure pip runs inside venv; chain properly.
• Non-root, pinned base, correct ENTRYPOINT.

Rationale: Build correctness and security.