- FolkQueue: json_encode instead of msgpack_pack for jobs.push RPC
  (no more PHP msgpack extension dependency)
- FolkJobHandler: extract payload from {payload: "..."} wrapper object
  sent by folk-plugin-jobs v0.3.0 via execute_value zero-copy path

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>