feat: add automatic updates for vibetyper, msty-studio, zellij-ps

- vibetyper/msty-studio: unversioned AppImage URLs → HEAD/Last-Modified
  check via custom update.sh, refreshes sha256 when upstream binary changes
- zellij-ps: switch to branch-tracking (master tip via Gitea API) since
  helper-scripts repo has no tags
- all three expose passthru.updateScript so the existing CI workflow
  discovers them via is_custom_update_script

pkgs/vibetyper/default.nix

@@ -1,3 +1,4 @@
+# last-modified: Fri, 24 Jul 2026 10:50:57 GMT
 {
   appimageTools,
   fetchurl,
@@ -6,6 +7,8 @@
 }: let
   pname = "vibetyper";
   version = "1.4.0";
+  # Upstream publishes to an unversioned URL — ./update.sh watches Last-Modified
+  # and refreshes the sha256 when the binary changes. Bump `version` manually.
   src = fetchurl {
     url = "https://cdn.vibetyper.com/releases/linux/VibeTyper.AppImage";
     sha256 = "sha256-p4MOTKbEMIUhwhyGSE/l6ucwpPjeTELJ0lX4TXrKf2Y=";
@@ -29,6 +32,8 @@ in
               --set VIBE_DISABLE_HYPRLAND_INDICATOR_NO_BLUR 1
     '';
 
+    passthru.updateScript = ./update.sh;
+
     meta = {
       description = "VibeTyper - AI-powered typing assistant";
       homepage = "https://vibetyper.com";