feat(desktop): add screen recording (task 0029)

Add a wf-recorder module, enabled by the desktop aggregator. Super+Shift+R
picks a region with slurp and toggles a video-only capture (no audio), stopped
with SIGINT so the file finalises, saved to ~/Videos/Recordings. Start and
saved notifications fire via notify-send.

A Waybar custom/recording widget samples the wf-recorder process once a second
and shows a video glyph while a capture runs.

modules/desktop/recording.nix

@@ -0,0 +1,54 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+# Keybound screen recording: pick a region, then toggle a video-only capture.
+let
+  cfg = config.modules.desktop.recording;
+  user = config.user.name;
+
+  slurp = "${pkgs.slurp}/bin/slurp";
+  wf-recorder = "${pkgs.wf-recorder}/bin/wf-recorder";
+  notify-send = "${pkgs.libnotify}/bin/notify-send";
+  pgrep = "${pkgs.procps}/bin/pgrep";
+  pkill = "${pkgs.procps}/bin/pkill";
+  date = "${pkgs.coreutils}/bin/date";
+  mkdir = "${pkgs.coreutils}/bin/mkdir";
+
+  recDir = "$HOME/Videos/Recordings";
+
+  # A single key both starts and stops.
+  # A running wf-recorder is stopped with SIGINT so it finalises the file.
+  # Otherwise slurp picks a region and wf-recorder runs in the foreground until
+  # that stop arrives, so this instance lives for the whole recording and then
+  # reports it saved.
+  # No -a means no audio is captured.
+  toggle = pkgs.writeShellScript "screen-record-toggle" ''
+    if ${pgrep} -x wf-recorder >/dev/null; then
+      ${pkill} -INT -x wf-recorder
+      exit 0
+    fi
+
+    region=$(${slurp}) || exit 0
+    ${mkdir} -p "${recDir}"
+    file="${recDir}/recording-$(${date} +%Y%m%d-%H%M%S).mp4"
+
+    ${notify-send} -a "Screen recording" "Recording started" "Region capture, no audio."
+    ${wf-recorder} -g "$region" -f "$file"
+    ${notify-send} -a "Screen recording" "Recording saved" "$file"
+  '';
+in
+{
+  options.modules.desktop.recording.enable = lib.mkEnableOption "wf-recorder screen recording";
+
+  config = lib.mkIf cfg.enable {
+    home-manager.users.${user} = {
+      # $mod is defined by the compositor config these binds share.
+      wayland.windowManager.hyprland.settings.bind = [
+        "$mod SHIFT, R, exec, ${toggle}"
+      ];
+    };
+  };
+}