refactor(actors): complete StreamActor consolidation and legacy cleanup

Complete hard cut-over from legacy stream implementations to the new
consolidated StreamActor in app/src/actors/bridge/actors/stream/.

Changes:
- Updated app.rs to import StreamActor from bridge/actors/stream location
- Updated actors/mod.rs exports to use new consolidated implementation
- Removed legacy governance_stream directory (10 files)
- Removed legacy stream_actor.rs and stream_actor_metrics.rs files
- All stream functionality now centralized in single consolidated actor

The new StreamActor provides comprehensive capabilities including AlysActor
trait compatibility, advanced configuration, gRPC protocol handling,
exponential backoff reconnection, request tracking, and extensive testing.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: michaelgpt