Add real-time log streaming API

## Motivation

- Enable following logs in real-time via `kubectl logs -f`. Depends on full log capture.

## Required Features

- Real-time log streaming endpoint
- WebSocket or long-polling delivery
- Support tail (`--tail N`) and since (`--since`) filters

## Impact

- **Manager**: Medium - Streaming endpoint
- **Agent**: Low - Log forwarding to stream

## Testing Scenarios

- Stream logs as they're generated
- Tail last N lines before streaming
- Filter by timestamp
- Handle client disconnect/reconnect
- Multiple concurrent stream subscribers

JIRA Issue: BA-3870