feat(api): implement StreamEvents gRPC handler

[Depo-dev]

Summary

EventsServiceImpl::stream_events currently returns Status::unimplemented. Needs a live Redis Streams consumer that fans out matching events to connected gRPC clients.

Acceptance Criteria

• Inject a redis::aio::ConnectionManager into EventsServiceImpl
• On each client connection, spawn a tokio task that does XREAD BLOCK 0 STREAMS trident:events $ in a loop
• Filter events by contract_id and/or topic_0 from StreamEventsRequest (if set)
• Send matching events down a tokio::sync::mpsc channel; return ReceiverStream to tonic
• Clean up the Redis reader task when the client disconnects (stream closed)
• Integration test: publish a synthetic event to Redis, assert it arrives on a connected stream client

Files

crates/api/src/services/events.rs, crates/api/src/main.rs