goyplex: netbird from a fresher nixpkgs pin (0.81.x) to match the 0.81 server

hosts/goyplex-vm/custom.nix

@@ -1,8 +1,17 @@
 # per-host overrides: static IP for the k3s edge node
 # LAN: 10.0.1.0/24, gw 10.0.1.1, DNS pas 10.0.1.45 + 1.1.1.1
-{ ... }:
+{ inputs, pkgs, ... }:
 
 {
+  # netbird client from a fresher nixpkgs pin. The system nixpkgs (locked
+  # 2026-09-04) ships netbird 0.78.1 while the k3s server runs the floating
+  # 0.81.x image; that skew breaks network/exit-route pushes to this peer.
+  nixpkgs.overlays = [
+    (final: prev: {
+      netbird = inputs.nixpkgs-netbird.legacyPackages.${final.stdenv.hostPlatform.system}.netbird;
+    })
+  ];
+
   networking.networkmanager.ensureProfiles.environmentFiles = [ ];
   networking.networkmanager.ensureProfiles.profiles = {
     "ens18-static" = {