add prometheus metrics

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+# Prometheus and Grafana Setup
+
+This guide shows how to configure Prometheus and Grafana to monitor ngit-grasp.
+
+## Prerequisites
+
+- ngit-grasp running with metrics enabled (default: `--metrics-enabled true`)
+- Prometheus server
+- Grafana (optional, for dashboards)
+
+## Verify Metrics Endpoint
+
+First, verify that ngit-grasp is exposing metrics:
+
+```bash
+curl http://localhost:8080/metrics
+```
+
+You should see Prometheus-formatted metrics like:
+
+```
+# HELP ngit_websocket_connections_active Current active WebSocket connections
+# TYPE ngit_websocket_connections_active gauge
+ngit_websocket_connections_active 5
+
+# HELP ngit_git_operations_total Git operations by type and status
+# TYPE ngit_git_operations_total counter
+ngit_git_operations_total{operation="clone",status="success"} 42
+```
+
+## NixOS Configuration
+
+### Prometheus
+
+Add ngit-grasp as a scrape target:
+
+```nix
+services.prometheus = {
+  enable = true;
+  scrapeConfigs = [
+    {
+      job_name = "ngit-grasp";
+      static_configs = [{
+        targets = [ "localhost:8080" ];  # ngit-grasp bind address
+      }];
+      scrape_interval = "15s";
+      metrics_path = "/metrics";
+    }
+  ];
+};
+```
+
+### Grafana with Prometheus Datasource
+
+```nix
+services.grafana = {
+  enable = true;
+  settings.server.http_port = 3000;
+  
+  provision.datasources.settings.datasources = [{
+    name = "Prometheus";
+    type = "prometheus";
+    url = "http://localhost:9090";
+    isDefault = true;
+  }];
+  
+  # Optional: provision the ngit-grasp dashboard
+  provision.dashboards.settings.providers = [{
+    name = "ngit-grasp";
+    options.path = "/path/to/ngit-grasp/docs/grafana";
+  }];
+};
+```
+
+## Docker Compose Configuration
+
+For non-NixOS deployments:
+
+```yaml
+version: '3.8'
+services:
+  prometheus:
+    image: prom/prometheus:latest
+    volumes:
+      - ./prometheus.yml:/etc/prometheus/prometheus.yml
+    ports:
+      - "9090:9090"
+    
+  grafana:
+    image: grafana/grafana:latest
+    ports:
+      - "3000:3000"
+    volumes:
+      - ./docs/grafana:/var/lib/grafana/dashboards
+    environment:
+      - GF_DASHBOARDS_DEFAULT_HOME_DASHBOARD_PATH=/var/lib/grafana/dashboards/ngit-grasp-dashboard.json
+```
+
+With `prometheus.yml`:
+
+```yaml
+global:
+  scrape_interval: 15s
+
+scrape_configs:
+  - job_name: 'ngit-grasp'
+    static_configs:
+      - targets: ['host.docker.internal:8080']  # or your ngit-grasp host
+    metrics_path: /metrics
+```
+
+## Import Dashboard
+
+1. Open Grafana at `http://localhost:3000`
+2. Go to **Dashboards** → **Import**
+3. Upload `docs/grafana/ngit-grasp-dashboard.json`
+4. Select your Prometheus datasource
+5. Click **Import**
+
+## Key Metrics to Monitor
+
+### Connection Health
+- `ngit_websocket_connections_active` - Current active connections
+- `ngit_websocket_unique_ips` - Number of unique client IPs
+- `ngit_websocket_flagged_abusers` - IPs exceeding connection threshold
+
+### Git Operations
+- `ngit_git_operations_total` - Operations by type (clone/fetch/push) and status
+- `ngit_git_bytes_total` - Bandwidth by direction (in/out)
+- `ngit_git_top_repos_bytes` - Top N repositories by bandwidth
+
+### Nostr Events
+- `ngit_events_received_total` - Events received by kind
+- `ngit_events_stored_total` - Events successfully stored
+- `ngit_events_rejected_total` - Events rejected by reason
+
+### System
+- `ngit_uptime_seconds` - Server uptime
+- `ngit_build_info` - Version and commit info
+- `ngit_repositories_total` - Total hosted repositories
+
+## Example Alerts
+
+Add to your Prometheus alerting rules:
+
+```yaml
+groups:
+  - name: ngit-grasp
+    rules:
+      - alert: HighConnectionCount
+        expr: ngit_websocket_connections_active > 100
+        for: 5m
+        labels:
+          severity: warning
+        annotations:
+          summary: "High number of WebSocket connections"
+          
+      - alert: AbusiveIPs
+        expr: ngit_websocket_flagged_abusers > 0
+        for: 1m
+        labels:
+          severity: warning
+        annotations:
+          summary: "{{ $value }} IPs flagged for excessive connections"
+          
+      - alert: PushAuthorizationFailures
+        expr: rate(ngit_git_operations_total{operation="push",status="denied"}[5m]) > 0.1
+        for: 5m
+        labels:
+          severity: info
+        annotations:
+          summary: "Elevated push authorization failures"
+```
+
+## See Also
+
+- [Monitoring Overview](../explanation/monitoring.md) - Architecture and design
+- [Configuration Reference](../reference/configuration.md) - All config options
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