fix(multiplayer): validate legacy connection leases

server/migrations/0012_validate_connection_leases.sql

@@ -0,0 +1,5 @@
+-- Migration 0011 used NOT VALID so the new check protected concurrent writes
+-- while its backfill completed. Validate separately so an upgraded database
+-- cannot silently retain an impossible pre-lease connection state.
+ALTER TABLE match_participants
+    VALIDATE CONSTRAINT match_participants_connection_lease;