PixDala alpha.38 prepared patch

This archive contains the files changed for the next release.
Changes: unique participant counting, cell-occupation audio, completion overlay stacking, and client-side propagation of server-authoritative destruction start for already-open viewers.

Base: current user-provided PixDala alpha.37 archive.
Local automated verification: npm run check -> 10 unit, 17 integration, 8 API; structure and JS syntax checks passed (35/35 test cases).

Do not deploy this patch by copying files directly to the VPS. Replace the corresponding files in the Windows repository, run npm.cmd run check, review Git diff, then commit/tag/deploy through the normal Git workflow.