nwg-panel: enable per-app volume controls

hosts/common/programs/default.nix

@@ -99,6 +99,7 @@
     ./obsidian.nix
     ./offlineimap.nix
     ./open-in-mpv.nix
+    ./pactl.nix
     ./pipewire.nix
     ./planify.nix
     ./portfolio-filemanager.nix

hosts/common/programs/nwg-panel/default.nix

@@ -84,6 +84,10 @@ in
       strictDeps = true;
     });
 
+    suggestedPrograms = [
+      "pactl"  # pactl required by `per-app-volume` component.
+    ];
+
     # fs.".config/nwg-panel/config".symlink.target = ./config;
     # fs.".config/nwg-panel/style.css".symlink.target = ./style.css;
     fs.".config/nwg-panel/config".symlink.target = pkgs.substituteAll {
@@ -99,6 +103,7 @@ in
           "brightness"
         ] ++ [
           "volume"
+          "per-app-volume"
         ] ++ lib.optionals cfg.config.battery [
           "battery"
         ]

hosts/common/programs/pactl.nix

@@ -0,0 +1,6 @@
+{ pkgs, ... }:
+{
+  sane.programs.pactl = {
+    packageUnwrapped = pkgs.linkIntoOwnPackage pkgs.pulseaudio "bin/pactl";
+  };
+}