sw: bump cache to v5 to force arena UDP listener refresh
The previous fix added channel.on("arena:snap") + channel.on("squash:move")
to lib/udp.mjs, but stale-while-revalidate meant existing clients kept
running the cached copy without the new listeners. Bumping CACHE_NAME
triggers the activate handler to delete ac-modules-v4 and fetch fresh.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>