feat: add README for Pi Monitoring Stack setup and usage instructions

setup/pi-monitoring/README.md

@@ -0,0 +1,61 @@
+# Pi Monitoring Stack
+
+Purpose: turn a Raspberry Pi 4 (8GB) into a low-power monitoring/control plane for your Gitea migration environment.
+
+This module deploys:
+- Portainer (single admin view)
+- Grafana (dashboards)
+- Prometheus (metrics)
+- Uptime Kuma (service checks)
+- Node Exporter + cAdvisor (Pi host + container metrics)
+
+## Folder Contents
+
+- `bootstrap_pi.sh`: first-time host prep (packages, Docker, firewall, hardening)
+- `mount_ssd.sh`: format/mount SSD and create persistent data paths
+- `deploy_stack.sh`: deploy monitoring stack with Docker Compose
+- `upgrade_stack.sh`: pull new images and recreate stack
+- `backup_stack.sh`: backup stack data/config to `OPS_ROOT/backups`
+- `restore_stack.sh`: restore from backup archive
+- `status.sh`: show service status and endpoint reachability
+- `teardown_stack.sh`: stop/remove stack; optionally delete stack data
+- `install_portainer_agent_remote.sh`: install Portainer Agent on Fedora/Unraid
+- `docker-compose.yml`: stack definition
+- `stack.env.example`: environment template
+- `prometheus/prometheus.yml`: Prometheus config
+- `USAGE_GUIDE.md`: full setup and operations guide
+
+## Quick Start
+
+Run on the Raspberry Pi host:
+
+```bash
+cd /path/to/gitea-migration/setup/pi-monitoring
+
+./bootstrap_pi.sh --yes
+./mount_ssd.sh --device=/dev/sda1 --yes
+
+cp stack.env.example stack.env
+# edit stack.env and set a strong GRAFANA_ADMIN_PASSWORD
+
+./deploy_stack.sh --yes
+./status.sh
+```
+
+Then from your admin machine, install Portainer agent on remote Docker hosts:
+
+```bash
+./install_portainer_agent_remote.sh --host=<unraid-ip> --user=<unraid-user> --port=22 --yes
+./install_portainer_agent_remote.sh --host=<fedora-ip> --user=<fedora-user> --port=22 --yes
+```
+
+In Portainer UI (`https://<pi-ip>:9443`), add environments using:
+- `tcp://<unraid-ip>:9001`
+- `tcp://<fedora-ip>:9001`
+
+## Security Notes
+
+- `stack.env` contains secrets; do not commit it.
+- Portainer Agent exposes Docker control on `9001`; keep it inside trusted LAN/VPN.
+- Keep UFW enabled and only expose required ports.
+- Use SSD for durability; avoid long-term DB workloads on SD card.