Load-test the public instance and document capacity

[7akob]

The public instance at skood.jkb.app runs on a small box and has never been load-tested. The README currently hedges with "if it's busy, self-host". Let's replace the hedge with numbers.

What to measure

• Concurrent WebSocket connections and rooms before latency or errors degrade. Note that the transport is WebSocket only, so every client holds a persistent socket and there is no polling fallback to soak up overflow
• Memory per room and per socket (rooms are a single in-memory object in server.js)
• Broadcast fan-out cost in big rooms, since every play, pause and seek hits every socket in the room

A simple harness would do: N socket.io-client connections joining M rooms, each emitting a play or pause every few seconds. Even rough numbers from the actual VPS help.

What to do with the numbers

• Document real capacity in the README's hosted-instance note, replacing the hedge
• Consider a MAX_ROOMS env guard: when the cap is hit, new join attempts get a friendly system message saying the instance is full and self-hosting is two commands, instead of everyone degrading together
• Rooms are ephemeral by design and a restart wipes them; if the instance restarts often, note that in the README too

Not in scope

Horizontal scaling and Redis adapters. A second instance would split rooms, and it cuts against the tiny-by-design philosophy. If one box can't hold the load, the answer is more self-hosting, not more infrastructure.