Add metrics monitoring stack with VictoriaMetrics, Grafana, and node_exporter

Implement complete monitoring infrastructure following rick-infra principles:

Components:
- VictoriaMetrics: Prometheus-compatible TSDB (7x less RAM usage)
- Grafana: Visualization dashboard with Authentik OAuth/OIDC integration
- node_exporter: System metrics collection (CPU, memory, disk, network)

Architecture:
- All services run as native systemd binaries (no containers)
- localhost-only binding for security
- Grafana uses native OAuth integration with Authentik (not forward_auth)
- Full systemd security hardening enabled
- Proxied via Caddy at metrics.jnss.me with HTTPS

Role Features:
- Unified metrics role (single role for complete stack)
- Automatic role mapping via Authentik groups:
  - authentik Admins OR grafana-admins -> Admin access
  - grafana-editors -> Editor access
  - All others -> Viewer access
- VictoriaMetrics auto-provisioned as default Grafana datasource
- 12-month metrics retention by default
- Comprehensive documentation included

Security:
- OAuth/OIDC SSO via Authentik
- All metrics services bind to 127.0.0.1 only
- systemd hardening (NoNewPrivileges, ProtectSystem, etc.)
- Grafana accessible only via Caddy HTTPS proxy

Documentation:
- roles/metrics/README.md: Complete role documentation
- docs/metrics-deployment-guide.md: Step-by-step deployment guide

Configuration:
- Updated rick-infra.yml to include metrics deployment
- Grafana port set to 3001 (Gitea uses 3000)
- Ready for multi-host expansion (designed for future node_exporter deployment to production hosts)

roles/metrics/tasks/main.yml

@@ -0,0 +1,20 @@
+---
+# =================================================================
+# Metrics Stack Deployment
+# =================================================================
+
+- name: Deploy VictoriaMetrics
+  ansible.builtin.include_tasks: victoriametrics.yml
+  tags: [metrics, victoriametrics]
+
+- name: Deploy node_exporter
+  ansible.builtin.include_tasks: node_exporter.yml
+  tags: [metrics, node_exporter]
+
+- name: Deploy Grafana
+  ansible.builtin.include_tasks: grafana.yml
+  tags: [metrics, grafana]
+
+- name: Deploy Caddy configuration for Grafana
+  ansible.builtin.include_tasks: caddy.yml
+  tags: [metrics, caddy]