test(FN-705): add comprehensive unit tests for IpcHost and IpcWorker
- Add IpcHost tests: constructor, sendCommand correlation, ping, event forwarding, malformed message handling, disconnection cascade, explicit cleanup
- Add IpcWorker tests: constructor validation, PING auto-response, command handler registration/dispatch, OK/ERROR responses, sendEvent/sendErrorEvent, shutdown idempotency
- Fix TypeScript type mismatch in mock ChildProcess.send signature
- Mock logger and process IPC to enable isolated unit testing without real child processes
- Cover edge cases: timeouts, disconnected sends, unknown commands, malformed messages
0ec0dab300