feat(amd): add opencode web server at opencode.amd.hoyer.world

Mirror of the sgx opencode setup: systemd service on port 4196 fronted
by nginx with a per-host ACME cert (DNS-01 via internetbs). Adds amd
key + path rule to .sops.yaml so secrets under .secrets/amd/ encrypt
for the host.

systems/x86_64-linux/amd/nginx.nix

@@ -0,0 +1,18 @@
+{
+  ...
+}:
+{
+  services.nginx.virtualHosts = {
+    "opencode.amd.hoyer.world" = {
+      enableACME = true;
+      forceSSL = true;
+      locations."/" = {
+        proxyPass = "http://127.0.0.1:4196";
+        proxyWebsockets = true;
+        extraConfig = ''
+          proxy_buffering off;
+        '';
+      };
+    };
+  };
+}