chore: add AGENTS.md for opencode agents

AGENTS.md

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+# Agents
+
+This role/playbook manages Proxmox VE cluster updates with Ceph maintenance mode handling.
+
+## Role Analysis
+
+- **Type**: Infrastructure automation (playbook + tasks)
+- **OS Support**: Proxmox VE 9
+- **Deployment Method**: Direct SSH to Proxmox nodes
+- **Scope**: Cluster update automation with HA support
+
+## Key Features
+
+- Serial node updates (one at a time)
+- Ceph maintenance mode integration
+- Cluster configuration management
+
+## Tags
+
+| Tag | Purpose |
+|-----|---------|
+| `configure-cluster` | Configure Proxmox cluster nodes |
+| `update-cluster` | Update Proxmox cluster (with Ceph handling) |
+
+## Testing
+
+```bash
+ansible-lint
+molecule test
+```