Add grok-bot 0.18.0

Package the official Grok Bot Linux .deb (internal name: sand) for Arch.
Wraps /opt/Grok Bot/sand with a Wayland launcher and grok-bot desktop entry.

Linux has no latest feed; update-pkgver.sh resolves version+commit from the
darwin-arm64 sand feed and HEAD-checks the Linux deb before pinning.

pkgbuilds/grok-bot/update-pkgver.sh

@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+# Resolve current Grok Bot stable from Cursor's update feed and pin PKGBUILD.
+# Linux has no latest alias (linux-x64 feed returns 204). The darwin-arm64
+# sand feed publishes version + commit; the Linux .deb lives at the same commit.
+# Darwin can ship first — HEAD-check the Linux URL and fail loudly if 404.
+set -euo pipefail
+
+PKGBUILD_PATH="${1:-PKGBUILD}"
+[[ -f "${PKGBUILD_PATH}" ]] || { echo "Error: PKGBUILD not found at '${PKGBUILD_PATH}'" >&2; exit 1; }
+
+FEED='https://api2.cursor.sh/updates/api/update/darwin-arm64/sand/0.0.0/00000000-0000-0000-0000-000000000000/stable'
+json="$(curl -fsSL -H 'cache-control: no-cache' "${FEED}")"
+
+ver="$(jq -er '.name // .version' <<<"${json}")"
+feed_url="$(jq -er '.url' <<<"${json}")"
+commit="$(sed -nE 's@.*/(grokbot|sand)/stable/([0-9a-f]{40})/.*@\2@p' <<<"${feed_url}")"
+
+[[ -n "${ver}" && -n "${commit}" ]] || {
+  echo "Error: could not parse version/commit from feed: ${json}" >&2
+  exit 1
+}
+
+deb_url="https://downloads.cursor.com/grokbot/stable/${commit}/linux/x64/Grok_Bot_${ver}.deb"
+code="$(curl -fsSIL -o /dev/null -w '%{http_code}' "${deb_url}")"
+[[ "${code}" == "200" ]] || {
+  echo "Error: Linux deb not fetchable (${code}): ${deb_url}" >&2
+  exit 1
+}
+
+tmp="$(mktemp)"
+trap 'rm -f "${tmp}"' EXIT
+curl -fL --retry 3 -o "${tmp}" "${deb_url}"
+sum="$(sha256sum "${tmp}" | awk '{print $1}')"
+
+current_ver="$(sed -nE 's/^pkgver=([^[:space:]#]+).*/\1/p' "${PKGBUILD_PATH}" | head -n1)"
+
+sed -i -E \
+  -e "s/^_commit=.*/_commit=${commit}/" \
+  -e "s/^pkgver=.*/pkgver=${ver}/" \
+  -e "0,/^[[:space:]]*'[0-9a-f]{64}'/s//    '${sum}'/" \
+  "${PKGBUILD_PATH}"
+
+if [[ "${ver}" != "${current_ver}" ]]; then
+  sed -i -E 's/^pkgrel=.*/pkgrel=1/' "${PKGBUILD_PATH}"
+fi
+
+echo "${ver} ${commit}"
+echo "${deb_url}"
+echo "${sum}"