Initial metrics skill with aggregation

SKILL.md

@@ -0,0 +1,73 @@
+---
+name: metrics
+description: Metrics aggregator with system and skill metrics
+metadata:
+  version: "1.0.0"
+  vibestack:
+    main: false
+    metrics-port: 9090
+---
+
+# Metrics Skill
+
+Aggregates metrics from system (node_exporter) and other skills into a single `/metrics` endpoint.
+
+## Features
+
+- System metrics via node_exporter (CPU, memory, disk, network)
+- Auto-discovers skills that expose metrics
+- Single aggregated endpoint for Prometheus scraping
+- Auto-registers with Caddy if present
+
+## How Skills Expose Metrics
+
+Skills can expose metrics by adding to their SKILL.md:
+
+```yaml
+metadata:
+  vibestack:
+    metrics-port: 8080
+```
+
+Or by setting environment variable:
+```bash
+METRICS_PORT_myskill=8080
+```
+
+The aggregator will scrape `localhost:{port}/metrics` for each discovered skill.
+
+## Configuration
+
+| Variable | Description | Default |
+|----------|-------------|---------|
+| `METRICS_PORT` | Aggregator port | `9090` |
+| `NODE_EXPORTER_PORT` | node_exporter port | `9100` |
+| `METRICS_DOMAIN` | Domain for Caddy auto-config | (none) |
+| `METRICS_PATH` | URL path for metrics | `/metrics` |
+
+## Collected Metrics
+
+### System (node_exporter)
+- `node_cpu_*` - CPU usage
+- `node_memory_*` - Memory usage
+- `node_disk_*` - Disk I/O
+- `node_network_*` - Network I/O
+- `node_filesystem_*` - Filesystem usage
+
+### Per-Skill
+Each skill's metrics are prefixed with the skill name:
+```
+# From ttyd skill
+ttyd_connections_active 5
+ttyd_sessions_total 123
+```
+
+## Usage
+
+```bash
+# Scrape aggregated metrics
+curl http://localhost:9090/metrics
+
+# With Caddy proxy
+curl https://metrics.example.com/metrics
+```