chore: add AGENTS.md for opencode agents

AGENTS.md

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+# Agents
+
+This role manages core OS components and defaults tailored for Siempie infrastructure. This is the foundational role for all Debian/Ubuntu systems.
+
+## Role Analysis
+
+- **Type**: Base system configuration role
+- **OS Support**: Debian 12, Debian 13, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, Alpine 3.23
+- **Deployment Method**: Direct (not Docker-based)
+- **Scope**: Comprehensive system configuration
+
+## Key Variables
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `apt_automatic_reboot_time` | `03:45` | Automated reboot time |
+| `apt_automatic_reboot` | `true` | Enable automated reboots |
+| `apt_enable_universe` | `true` | Enable Ubuntu universe repo |
+| `firewall_enable` | `true` | Enable firewall |
+| `ntp_server` | `time.cloudflare.com` | NTP server |
+| `timezone` | `Europe/Amsterdam` | System timezone |
+| `swap` | `false` | Enable swap |
+
+## Available Tags
+
+- `apt` - APT package management
+- `apt-update` - APT update
+- `apt-cleanup` - APT cleanup
+- `cron` - Cron jobs
+- `environment-file` - Environment configuration
+- `hostname` - Hostname management
+- `firewall` - UFW firewall
+- `journald` - Systemd journal config
+- `locale` - Locale settings
+- `ntp` - NTP/Chrony configuration
+- `sshd` - SSH daemon config
+- `swap` - Swap configuration
+- `sysctl` - Kernel parameters
+- `systemctl` - Systemd units
+- `timezone` - Timezone settings
+- `usermanagement` - User management
+
+## Testing
+
+```bash
+ansible-lint
+molecule test
+```