feat(desktop): resolve media output paths through XDG user-dirs

Add a modules.desktop.userdirs module that declares the XDG user directories,
and route the recorder and screenshot tools through xdg-user-dir so their
output folders (Videos/Recordings, Pictures/Screenshots) follow one relocatable
source instead of a hardcoded $HOME path.

.claude/tasks/0029-screen-recording.md

@@ -34,7 +34,9 @@ No audio capture and no full-screen recording variant.
 - **No waybar `window-rewrite` icon.**
   wf-recorder is headless and slurp is a transient selection overlay, so neither owns a workspace window and the per-application icon convention does not apply.
 
-- **Recordings land in `~/Videos/Recordings`**, timestamped `recording-<date>.mp4`, with the directory created on first capture.
+- **Output paths follow XDG user-dirs.**
+  A new `modules.desktop.userdirs` declares the XDG user directories (home-manager `xdg.userDirs`), and the recorder resolves its base with `xdg-user-dir VIDEOS`, writing timestamped `recording-<date>.mp4` under `<Videos>/Recordings` (created on first capture).
+  The screenshot module (task 0028) was aligned to the same convention (`xdg-user-dir PICTURES` → `<Pictures>/Screenshots`), so relocating a directory is a one-line change to `xdg.userDirs` rather than an edit in each tool.
 
 - **Live capture is the irreducible manual step.**
   The build is green, the config parses under `Hyprland --verify-config`, and the indicator's idle/recording transitions are verified against a stand-in process; exercising a real slurp selection and wf-recorder capture needs a running session.

modules/desktop/desktop.nix

@@ -19,6 +19,7 @@ in
     modules.desktop.rofi.enable = lib.mkDefault true;
     modules.desktop.screenshot.enable = lib.mkDefault true;
     modules.desktop.terminal.enable = lib.mkDefault true;
+    modules.desktop.userdirs.enable = lib.mkDefault true;
     modules.desktop.theming.enable = lib.mkDefault true;
     modules.desktop.waybar.enable = lib.mkDefault true;
     modules.desktop.audio.enable = lib.mkDefault true;

modules/desktop/recording.nix

@@ -16,8 +16,7 @@ let
   pkill = "${pkgs.procps}/bin/pkill";
   date = "${pkgs.coreutils}/bin/date";
   mkdir = "${pkgs.coreutils}/bin/mkdir";
-
+  xdgUserDir = "${pkgs.xdg-user-dirs}/bin/xdg-user-dir";
-  recDir = "$HOME/Videos/Recordings";
 
   # A single key both starts and stops.
   # A running wf-recorder is stopped with SIGINT so it finalises the file.
@@ -32,8 +31,9 @@ let
     fi
 
     region=$(${slurp}) || exit 0
-    ${mkdir} -p "${recDir}"
+    dir="$(${xdgUserDir} VIDEOS)/Recordings"
-    file="${recDir}/recording-$(${date} +%Y%m%d-%H%M%S).mp4"
+    ${mkdir} -p "$dir"
+    file="$dir/recording-$(${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"

modules/desktop/screenshot.nix

@@ -13,8 +13,7 @@ let
   grimblast = "${pkgs.grimblast}/bin/grimblast";
   satty = "${pkgs.satty}/bin/satty";
   wl-copy = "${pkgs.wl-clipboard}/bin/wl-copy";
-
+  xdgUserDir = "${pkgs.xdg-user-dirs}/bin/xdg-user-dir";
-  shotDir = "$HOME/Pictures/Screenshots";
 
   # satty is the annotation step, and its copy action is set to save as well,
   # so a single keystroke through it lands the shot in both the clipboard and a
@@ -22,10 +21,11 @@ let
   capture =
     target:
     pkgs.writeShellScript "screenshot-${target}" ''
-      mkdir -p ${shotDir}
+      dir="$(${xdgUserDir} PICTURES)/Screenshots"
+      mkdir -p "$dir"
       ${grimblast} save ${target} - \
         | ${satty} --filename - \
-          --output-filename "${shotDir}/screenshot-%Y%m%d-%H%M%S.png" \
+          --output-filename "$dir/screenshot-%Y%m%d-%H%M%S.png" \
           --copy-command ${wl-copy} \
           --save-after-copy \
           --early-exit \

modules/desktop/userdirs.nix

@@ -0,0 +1,16 @@
+{ config, lib, ... }:
+# Declares the XDG user directories, so a tool that queries them lands in a
+# well-known folder a host can relocate from one place.
+let
+  cfg = config.modules.desktop.userdirs;
+  user = config.user.name;
+in
+{
+  options.modules.desktop.userdirs.enable = lib.mkEnableOption "XDG user directories";
+
+  config = lib.mkIf cfg.enable {
+    # enable writes ~/.config/user-dirs.dirs from the option defaults, which
+    # xdg-user-dir then reads.
+    home-manager.users.${user}.xdg.userDirs.enable = true;
+  };
+}