Number('') makes an empty members/maxMembers render as 0 / 8 in the room #823

What is wrong

An empty members/maxMembers is shown as a real zero.

plugins/social/client.js:895-899:

const members = seen.members === undefined || seen.members === null ? NaN : Number(seen.members)
const maxMembers = seen.maxMembers === undefined || seen.maxMembers === null ? NaN : Number(seen.maxMembers)
const people = Number.isFinite(members) && Number.isFinite(maxMembers) ? `${members} / ${maxMembers} in the room` : …

Number('') is 0 (and so is Number(' ')), and '' is neither undefined nor null, so a server that sends an empty string produces 0 / 8 in the room — a room that looks empty when the count is simply unknown.

Expected behaviour

Only a value that actually reads as a number counts: a trimmed, non-empty string that parses to a finite number. '', ' ', 'eight' are "not sent" — the line falls back the same way it does for null. A real 0 (0 or '0') still renders 0 / 8, because an empty room is a real state.

Acceptance

1. A fixture with members: '', maxMembers: 8 renders no 0 / 8 (the members half is treated as missing, so the one-number fallback applies, or the line disappears if both are missing).
2. A fixture with members: '0', maxMembers: 8 renders 0 / 8 in the room.
3. Whitespace (' 8 ') is either trimmed to 8 or treated as missing — pinned by a test either way, not left ambiguous.
4. npm test in plugins/social green.

Kill conditions

• Number(x) || NaN: turns a legitimate 0 into "missing".
• parseInt: accepts '8abc' as 8.
• Requiring both numbers before showing anything: that changes the one-number behaviour the issue asked for.
• Fixing it in the server by sanitising the payload: the client already receives arbitrary values from older servers.

Out of scope

• cleanRoomName's marker loop and the repeat-preview item.
• The server's previewInvite return shape (that is Face room invites: previewInvite has three layers and no client, so a join never shows the room first #798's contract, already merged).