feat(core): Redis queue implementation for EventBus

[crrow]

Context

Architecture design (docs/design/architecture.md line 34) specifies Queue as Redis Streams, RabbitMQ, or SQS for async job delivery. MetaService needs to publish cancellation/deletion events for Ingestor to consume. Currently using LogEventBus placeholder.

Acceptance Criteria

• Implement RedisEventBus that implements the EventBus trait
• Publish events to Redis Streams
• Ingestor consumes events and cancels in-flight processing
• Feature-gated behind redis cargo feature flag

Dependencies

• EventBus trait (to be added in metaservice alignment work)