fix(social): robot blocks

Blocking an auto-match opponent who is secretly a pooled robot is recorded  instead in a separate `robot_blocks` table.

Now blocking behaves the same in that game (struck name, hidden composer) and lists the blocked opponent under the name you saw, but is recorded only against that game — the disguise holds, the shared robot is never globally blocked, and the matchmaker keeps pairing you with robots (so you can never block yourself out of opponents).

- the shared robot account is never put in `blocks`
- the matchmaker keeps it free and it is not blocked under its other per-game names
- the blocked list and the in-game card still show it by joining that table; an unblock deletes the row

ui/src/game/ChatScreen.svelte

@@ -17,8 +17,10 @@
   let busy = $state(false);
   let tick = $state(0);
   // The opponents the viewer has blocked: when every opponent is blocked the composer is hidden
-  // (only the chat log remains), matching the backend guard that rejects messaging a blocked peer.
+  // (only the chat log remains). blockedIds are blocked humans (by account); blockedRobotSeats are
+  // the seats of blocked disguised robots in this game (a robot block is per game+seat).
   let blockedIds = $state(new Set<string>());
+  let blockedRobotSeats = $state(new Set<number>());
 
   const myId = $derived(app.session?.userId ?? '');
   const isMyTurn = $derived(
@@ -40,7 +42,10 @@
     const v = view;
     if (!v) return false;
     const opponents = v.game.seats.filter((s) => s.seat !== v.seat && !!s.accountId);
-    return opponents.length > 0 && opponents.every((s) => blockedIds.has(s.accountId));
+    return (
+      opponents.length > 0 &&
+      opponents.every((s) => blockedIds.has(s.accountId) || blockedRobotSeats.has(s.seat))
+    );
   });
   const nudgeCooldownSecs = 3600;
   // The nudge is one-per-hour-per-game and clears once the player chats (engagement); the
@@ -80,7 +85,8 @@
     if (app.profile?.isGuest) return;
     try {
       const bl = await gateway.blocksList();
-      blockedIds = new Set(bl.map((b) => b.accountId));
+      blockedIds = new Set(bl.blocked.map((b) => b.accountId));
+      blockedRobotSeats = new Set(bl.robots.filter((r) => r.gameId === id).map((r) => r.seat));
     } catch {
       /* best-effort */
     }