Initial loki skill with promtail auto-discovery

SKILL.md

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+---
+name: loki
+description: Log aggregation with Loki and Promtail
+metadata:
+  version: "1.0.0"
+  vibestack:
+    main: false
+    metrics-port: 3100
+---
+
+# Loki Skill
+
+Log aggregation using [Grafana Loki](https://grafana.com/oss/loki/) with Promtail for log shipping.
+
+## Features
+
+- Lightweight log storage (indexes labels, not content)
+- Auto-discovers skill logs from supervisor
+- Prometheus-compatible metrics
+- LogQL query language
+- Auto-registers with Caddy if present
+
+## Architecture
+
+```
+supervisor logs ──► promtail ──► loki ──► /loki/api/v1/query
+   /var/log/supervisor/*.log      :3100
+```
+
+## Configuration
+
+| Variable | Description | Default |
+|----------|-------------|---------|
+| `LOKI_PORT` | Loki API port | `3100` |
+| `LOKI_DATA_DIR` | Data storage directory | `/data/loki` |
+| `LOKI_RETENTION` | Log retention period | `168h` (7 days) |
+| `LOKI_DOMAIN` | Domain for Caddy auto-config | (none) |
+| `SUPERVISOR_LOG_DIR` | Where to find skill logs | `/var/log/supervisor` |
+
+## Querying Logs
+
+### Via API
+
+```bash
+# All logs from last hour
+curl -G "http://localhost:3100/loki/api/v1/query_range" \
+  --data-urlencode 'query={job="skills"}' \
+  --data-urlencode 'start=1h'
+
+# Logs from specific skill
+curl -G "http://localhost:3100/loki/api/v1/query_range" \
+  --data-urlencode 'query={skill="caddy"}'
+
+# Search for errors
+curl -G "http://localhost:3100/loki/api/v1/query_range" \
+  --data-urlencode 'query={job="skills"} |= "error"'
+```
+
+### LogQL Examples
+
+```logql
+# All skill logs
+{job="skills"}
+
+# Specific skill
+{skill="ttyd"}
+
+# Filter by content
+{job="skills"} |= "error"
+{job="skills"} |~ "error|warn"
+
+# JSON parsing (if logs are JSON)
+{job="skills"} | json | level="error"
+```
+
+## Integration with Grafana
+
+Add Loki as a data source:
+- URL: `http://loki:3100` (or via Caddy proxy)
+- Access: Server
+
+## Metrics
+
+Loki exposes Prometheus metrics at `:3100/metrics`:
+- `loki_ingester_streams_created_total`
+- `loki_distributor_bytes_received_total`
+- `loki_querier_query_duration_seconds`