Add screen-recorder plugin; refactor Affinity

Introduce a new screen‑recorder plugin with default settings, key
bindings,
and a bar widget entry. Add a dedicated Affinity module, import it in
the
core defaults, and remove the previous package entry. Enable Affinity on
the Garand‑Desktop and Garand‑Laptop hosts while keeping it disabled on
the
default host. Update flake.lock to newer revisions and reorder the
hyprland exec‑once commands.

modules/core/affinity.nix

@@ -0,0 +1,14 @@
+{
+  pkgs,
+  lib,
+  config,
+  inputs,
+  ...
+}: {
+  options.affinity.enable = lib.mkEnableOption "Steam";
+
+  config = lib.mkIf config.affinity.enable {
+    nixpkgs.overlays = [inputs.affinity-nix.overlays.default];
+    environment.systemPackages = with pkgs; [affinity-v3];
+  };
+}