docs: establishing baseline security and tools

docs/convergence.md

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+# 🔧 Server Convergence
+
+After provisioning servers with Terraform, RailianceHosts uses **Ansible** to bring them into a secure and usable baseline state.  
+This process is called **convergence**.
+
+## What Convergence Does
+
+When you run `make converge`, Ansible connects to all declared hosts and applies baseline roles:
+
+- **User setup** → ensures the `admin` user exists with your SSH key and passwordless sudo
+- **Firewall** → configures `ufw` with sensible defaults (deny incoming, allow SSH)
+- **Hardening** → basic SSH daemon hardening, disable root login, disable password auth
+- **Tooling** → installs essential packages (htop, vim, git, curl, fail2ban, etc.)
+- **SOPS agent** → ensures decryption tooling (`age`, `sops`) is available on the host
+
+## Running Convergence
+
+```bash
+make converge
+```
+
+This will:
+1. Decrypt secrets locally (with your age key)
+2. Run the Ansible playbooks against all hosts in your `inventory/servers.yaml`
+3. Apply the baseline security and tooling configuration
+
+## Verifying
+
+Once convergence completes, you can test:
+
+```bash
+ssh admin@<server-ip>
+
+# Check sudo access without password
+sudo -n true && echo "✔ sudo OK"
+
+# Firewall status
+sudo ufw status
+
+# Installed tools
+htop --version
+```
+
+## Notes
+
+- Convergence is **idempotent**: re-running it will not break your server.
+- Only your workstation (control node) needs the age private key; hosts never see it.
+- Additional roles (e.g. WireGuard, Kubernetes, apps) can be layered later.