feat: add TMP3 support and fix shard probe lifecycle bug

Add Trivia Murder Party 3 (Playtest) ticker and seed data. Bind-mount
tickers.json in docker-compose so ticker changes take effect on restart
without image rebuilds.

Fix shard monitor probe poisoning game lifecycle state — the player-count
probe no longer sets gameFinished, which was preventing the main WS from
processing room/lock and room/exit for games like TMP3 that don't send
entity updates.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/utils/ecast-shard-client.js

@@ -172,8 +172,9 @@ class EcastShardClient {
                 this.playerCount = playerCount;
                 this.playerNames = playerNames;
               }
-            } else if (msg.opcode === 'error' && msg.result?.code === 2027) {
-              this.gameFinished = true;
+            } else if (msg.opcode === 'error') {
+              // Probe errors are transient — lifecycle is managed
+              // by the main connection and reconnect logic
             }
           } catch (_) {}
           clearTimeout(timeout);
@@ -562,6 +563,8 @@ class EcastShardClient {
         finalPlayerCount: this.playerCount,
       });
       activeShards.delete(`${this.sessionId}-${this.gameId}`);
+      this.gameFinished = true;
+      this.disconnect();
       return false;
     } finally {
       this.reconnecting = false;