feat: track WebSocket subscriptions in metrics

Add metrics tracking for WebSocket (NIP-01) subscriptions in addition
to existing gRPC subscription tracking.

Changes:
- Add Count() method to subscription.Manager
- Add MetricsRecorder interface to WebSocket handler
- Update subscription metrics when REQ/CLOSE messages processed
- Wire up metrics to WebSocket handler in main.go

Before: Only gRPC stream subscriptions were counted
After: Both gRPC and WebSocket subscriptions tracked accurately

This fixes the dashboard showing 0 subscriptions when clients connect
via WebSocket (e.g., nak req --stream).

0 files changed, 0 insertions, 0 deletions