A move names the round it was made for; a stale one is refused

The room counts rounds played and sends the count in its view; a page
sends it back with each move, and the server refuses a move whose count
is behind (a slow connection, a second click, a stale tab), or that has
no count at all (an old page, told to reload). Before, such a move was
taken as the move for the next round. Found in Dip's acceptance run.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Jm2auWk6RP71CjaAb4FMoG

CONVENTIONS.md

@@ -68,6 +68,11 @@ README.
   page, gamehall.kestrelsnest.social. A new game is added to the kit's
   `family.json` and given a card on that page in the blog repo; both are
   hand-kept.
+- **A move names the round it was made for.** The room counts rounds
+  played (`resolved` in its view), and a page sends that count with each
+  move; the server refuses a move whose count is behind, so a slow
+  connection, a second click or a stale tab can never be taken as the
+  move for the next round. A page without the count is told to reload.
 - **The hosting line** follows the family list in the about panel: the
   games are free and will stay free, the servers cost a few dollars a
   month, and ko-fi.com/kestrelsnest is where anyone may chip in. It says