docs: harden metal prerequisites and mark Fedora ADR superseded

docs/installation/production/prerequisites.md

@@ -26,6 +26,9 @@ By using this project you agree to [the license](../../reference/license.md).
     The initial controller is the machine used to bootstrap the cluster, we only need it once, you can use your laptop or desktop
 
 - A **Linux** machine with Nix and root access to run the [Nixie](https://github.com/khuedoan/nixie) PXE server, which binds privileged network ports.
+- The development shell (`nix develop`) provides `nixie` and the other install tools.
+- The Makefile picks the PXE interface from the default route. Set `PXE_INTERFACE` when the nodes are not reachable through that interface.
+- The SSH private key passed to `make metal` (default `~/.ssh/id_ed25519`) must be authorized in `metal/installer.nix` and `metal/configuration.nix`.
 
 ### Servers
 

docs/reference/architecture/decision-records.md

@@ -45,8 +45,9 @@ configuration is built from `metal/configuration.nix`.
   and [homecloud](https://github.com/khuedoan/homecloud), instead of being
   embedded in this repository.
 - The migration is still in progress. Nodes run the base NixOS configuration
-  only, and k3s clustering, secrets management, and GitOps bootstrap are not
-  implemented yet.
+  only. k3s clustering, secrets management, and GitOps bootstrap are not
+  implemented yet, and `make` still chains the cluster stages (`system`,
+  `external`, `smoke-test`) that this branch does not provision.
 
 ## Remove the Docker wrapper for Nix shell
 
@@ -218,6 +219,8 @@ Migrate documentation from mdBook to MkDocs (see commit `cd41343`).
 
 ## Choosing the base OS
 
+**Status**: superseded by [Switch metal provisioning from Fedora and Ansible to NixOS](#switch-metal-provisioning-from-fedora-and-ansible-to-nixos)
+
 **Context**
 
 I've tried several distributions, and each has advantages and disadvantages.