refactor(flake): centralize custom packages

configs/nixos/modules/desktop/session/waybar.nix

@@ -30,32 +30,7 @@ in
 
     home-manager.users.${config.user.name}.programs.waybar = {
       enable = true;
-      # Waybar 0.15.0 sends old Hyprland workspace dispatch commands.
-      # Use the fix commit until a release includes upstream PR #5013.
-      package = pkgs.waybar.overrideAttrs {
-        src = pkgs.fetchFromGitHub {
-          owner = "Alexays";
-          repo = "Waybar";
-          rev = "05945748dccce28bf96d26d8f64a9e69a8dd49ba";
-          hash = "sha256-51R3mIt8cLNvh/X5qe9vOqeJCj0U9KRyemVE5y+OhiU=";
-        };
-
-        postUnpack =
-          let
-            libcava = pkgs.fetchFromGitHub {
-              owner = "LukashonakV";
-              repo = "cava";
-              tag = "0.10.7";
-              hash = "sha256-zkyj1vBzHtoypX4Bxdh1Vmwh967DKKxN751v79hzmgQ=";
-            };
-          in
-          ''
-            pushd "$sourceRoot"
-            cp -R --no-preserve=mode,ownership ${libcava} subprojects/cava-0.10.7
-            patchShebangs .
-            popd
-          '';
-      };
+      package = pkgs.alexion.waybar;
 
       # A user service bound to graphical-session.target, which uwsm activates,
       # so the bar comes up with the session and no compositor exec-once.