Sync Centaur stream creation with the current API

[ecejas]

Why

psychobot-team/reflex#5193 removed base streams and made prompt required for stream creation. The Centaur 0.1.0 wrapper still accepts base_stream_id and sends the removed base_feed_id field, so those requests now fail against the strict production contract.

How

• Require --prompt in the CLI and a non-empty prompt in the Python client.
• Remove base_stream_id and base_feed_id from the client, CLI, skill, and tests.
• Add CLI coverage proving a missing prompt is rejected and a valid prompt/name pair maps to the current request body.
• Bump the installable tool and immutable overlay pin to 0.1.1.

Verification

• pytest -q — 23 passed.
• python -m build tools/productivity/ambush-streams — built the 0.1.1 sdist and wheel.
• Skill Creator quick_validate.py .agents/skills/manage-ambush-streams — passed.
• git diff --check — passed.