The mystery machine keeps its mood to itself

"Random" read as random ACTIONS, and a revealed random pick is barely
a mystery anyway. The fourth workshop button is now "mystery": the
server rolls the temperament and keeps it — the join line records it
for replay, the drive loop plays it, but the room tells the table
only "mystery". Roster and scoresheet show ⚙ mystery; the machine's
behavior is the only tell.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

packages/server/src/store.ts

@@ -28,6 +28,8 @@ export interface JoinLine {
   bot?: true;
   /** The automaton's temperament. */
   style?: string;
+  /** A mystery machine: the temperament is not revealed to the table. */
+  secret?: true;
 }
 
 export interface StartLine {