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/zellij-ps/update.sh

@@ -0,0 +1,75 @@
+#!/usr/bin/env nix-shell
+#!nix-shell --pure -i bash -p bash curl jq nix nix-prefetch cacert git
+set -euo pipefail
+
+# Update zellij-ps to the latest commit on the helper-scripts master branch.
+# The upstream repo (m3ta.dev/m3tam3re/helper-scripts) has no tags/releases,
+# so we track the tip of master via the Gitea API.
+#
+# This is a "branch-tracking" updater: always pulls the newest commit,
+# NOT a stable release. Suitable for personal script repos.
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+NIX_FILE="$SCRIPT_DIR/default.nix"
+
+DOMAIN="code.m3ta.dev"
+OWNER="m3tam3re"
+REPO="helper-scripts"
+BRANCH="master"
+
+echo "Fetching latest commit on $BRANCH of $DOMAIN/$OWNER/$REPO..."
+LATEST_SHA=$(curl -fsSL "https://$DOMAIN/api/v1/repos/$OWNER/$REPO/branches/$BRANCH" \
+  | jq -r '.commit.id')
+
+if [[ -z "$LATEST_SHA" ]]; then
+  echo "ERROR: Failed to fetch latest commit from $DOMAIN/$OWNER/$REPO" >&2
+  exit 1
+fi
+
+# Read current rev from the nix file
+CURRENT_SHA=$(awk '
+  /^[[:space:]]*rev = "/ {
+    gsub(/^[[:space:]]*rev = "/, "")
+    gsub(/".*/, "")
+    print
+    exit
+  }
+' "$NIX_FILE")
+
+echo "Current: ${CURRENT_SHA:0:10}"
+echo "Latest:  ${LATEST_SHA:0:10}"
+
+if [[ "$LATEST_SHA" == "$CURRENT_SHA" ]]; then
+  echo "Already at latest commit, nothing to do."
+  exit 0
+fi
+
+echo "==> Updating zellij-ps: ${CURRENT_SHA:0:10} -> ${LATEST_SHA:0:10}"
+
+# Compute new sha256 via nix-prefetch-url (matches existing sha256 = "..." style)
+ARCHIVE_URL="https://$DOMAIN/$OWNER/$REPO/archive/$LATEST_SHA.tar.gz"
+echo "Prefetching: $ARCHIVE_URL"
+HASH=$(nix-prefetch-url --unpack --type sha256 "$ARCHIVE_URL" 2>/dev/null)
+
+if [[ -z "$HASH" ]]; then
+  echo "ERROR: nix-prefetch-url failed" >&2
+  exit 1
+fi
+
+echo "New sha256: $HASH"
+
+# Update rev and sha256 in the nix file
+sed -i "s|^\([[:space:]]*\)rev = \"[^\"]*\";|\1rev = \"$LATEST_SHA\";|" "$NIX_FILE"
+sed -i "s|^\([[:space:]]*\)sha256 = \"[^\"]*\";|\1sha256 = \"$HASH\";|" "$NIX_FILE"
+
+echo "Updated $NIX_FILE"
+
+# Commit when inside a git repo
+NIXPKGS_ROOT=$(git -C "$SCRIPT_DIR" rev-parse --show-toplevel 2>/dev/null || true)
+if [[ -n "$NIXPKGS_ROOT" ]] && \
+   [[ -n "$(git -C "$NIXPKGS_ROOT" status --porcelain "$NIX_FILE")" ]]; then
+  SHORT="${LATEST_SHA:0:10}"
+  git -C "$NIXPKGS_ROOT" add "$NIX_FILE"
+  git -C "$NIXPKGS_ROOT" commit -m "zellij-ps: update helper-scripts to $SHORT"
+  echo "==> Committed"
+fi