pkgbuild: Add grok-bot-bin from official .deb

Temporary Arch/CachyOS packaging until upstream ships a native package.
Pulls Cursor's amd64 deb by commit from the linux-x64 update feed.
Includes update script and Gitea Actions for bump + makepkg release.

scripts/update.sh

@@ -0,0 +1,42 @@
+#!/usr/bin/env bash
+# Bump PKGBUILD/.SRCINFO when Cursor publishes a newer linux-x64 Grok Bot.
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+FEED='https://api2.cursor.sh/updates/api/update/linux-x64/sand/0.0.0/00000000-0000-0000-0000-000000000000/stable'
+resp=$(curl -fsSL "$FEED")
+version=$(jq -r .version <<<"$resp")
+commit=$(jq -r .url <<<"$resp" | sed -E 's#.*/stable/([^/]+)/.*#\1#')
+current=$(sed -n 's/^pkgver=//p' PKGBUILD)
+
+if [[ -z "$version" || "$version" == "null" || ! "$commit" =~ ^[0-9a-f]{40}$ ]]; then
+  echo "Could not parse update feed: $resp" >&2
+  exit 1
+fi
+if [[ "$version" == "$current" ]]; then
+  echo "Up to date at $version"
+  exit 0
+fi
+
+echo "Bump $current -> $version (commit $commit)"
+deb_url="https://downloads.cursor.com/grokbot/stable/${commit}/linux/x64/grok-bot_${version}_amd64.deb"
+tmp=$(mktemp)
+trap 'rm -f "$tmp"' EXIT
+curl -fsSL --retry 3 "$deb_url" -o "$tmp"
+sha=$(sha256sum "$tmp" | cut -d' ' -f1)
+
+sed -i \
+  -e "s/^pkgver=.*/pkgver=${version}/" \
+  -e "s/^_commit=.*/_commit=${commit}/" \
+  -e "s/^sha256sums=.*/sha256sums=('${sha}')/" \
+  PKGBUILD
+
+# Refresh .SRCINFO source URL + hashes without requiring makepkg.
+sed -i \
+  -e "s/^\\tpkgver = .*/\\tpkgver = ${version}/" \
+  -e "s#^\\tsource = https://downloads.cursor.com/grokbot/stable/.*/linux/x64/grok-bot_.*_amd64.deb#\\tsource = https://downloads.cursor.com/grokbot/stable/${commit}/linux/x64/grok-bot_${version}_amd64.deb#" \
+  -e "s/^\\tnoextract = grok-bot_.*_amd64.deb/\\tnoextract = grok-bot_${version}_amd64.deb/" \
+  -e "s/^\\tsha256sums = .*/\\tsha256sums = ${sha}/" \
+  .SRCINFO
+
+echo "Updated PKGBUILD and .SRCINFO to ${version} sha256=${sha}"