[Feature] Redis Streams Integration for Status Events

[yedidyakfir]

Description

Add Redis Streams support for durable status change events.

Blocked by: #40, #42, #43

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Tasks

• Research Redis Streams consumer groups API
• Design event schema: {signature_key, old_status, new_status, timestamp, signature_type}
• Implement stream publishing on TaskSignature.done() and TaskSignature.failed()
• Create consumer group utilities for the external service
• Add integration tests for stream reliability

Key Files

• /mageflow/signature/model.py
• /mageflow/signature/status.py