Say plainly that there is no player limit, and stop one classroom hitting it

The README heading read 'Two people, two browsers', which sounds like a
cap. It is not one: the server holds no game state at all, so any number
of people play independent games and the server only ever sees a
finished score. The only real cap is four to a game, and that is a
keyboard sharing the same stand rather than anything technical.

Checking that turned up a case where it would not have been true. A
classroom, an office or a household all arrive from one address, and the
submission limit of thirty an hour was low enough that a class finishing
together would have started losing scores to a 429. Raised to 120 and
verified with a burst of 130: the first 120 land, the rest are refused.
What actually keeps rubbish off the board is the plausibility check, not
this limit.

server/src/index.ts

@@ -53,7 +53,14 @@ interface Bucket {
 }
 const posts = new Map<string, Bucket>()
 const POST_WINDOW_MS = 60 * 60 * 1000
-const POST_LIMIT = 30
+/*
+ * Per address, per hour. Generous on purpose: a classroom, an office or a
+ * household all arrive from one address, and thirty was low enough that a
+ * class finishing a season together would have started losing scores to a
+ * 429. What actually keeps rubbish off the board is the plausibility check
+ * in validate.ts, not this - this only stops the database being hammered.
+ */
+const POST_LIMIT = 120
 
 function overPostLimit(ip: string): boolean {
   const now = Date.now()