Wire MultiCapture operation ID propagation

Feature: capture and reuse per-flow operation IDs
- Add Start test scripts for ChannelEstimation, RxMER, and OFDMA
- Extract operation_id from start responses with response-shape fallback
- Save IDs to collection vars and fallback to environment vars
- Set generic op_id for backward compatibility with existing flows
- Update Results, Status, and Stop URLs to use per-flow op-id vars
- Update MultiCapture analysis bodies to use per-flow operation_id
- Preserve visualizer sync integrity with no drift detected - 2026-02-28 22:37:16

Author: mgarcia01752