feat(visual): add multi-capture channel estimation echo-detection IFFT visual and tune chart readability

- add ChannelEstimation-Analysis-Echo-Detection-IFFT Postman visual from scratch (previous HTML was empty)
- standardize layout with centered header, optional Capture Time pill, and optional Device Info table
- render combined IFFT magnitude chart aligned by delay across channels
- render per-channel IFFT magnitude panels in a 2-column grid with direct-path and echo markers
- parse complex IFFT samples ([real, imag]) into magnitudes and preserve direct/echo bins during sampling
- include per-channel echo summary chips and echo table (when echoes exist)
- use a top-level TUNING section for chart heights and sampling caps (no scattered magic numbers)
- increase combined/per-channel chart heights and disable forced aspect ratio so waveforms are readable
- regenerate visual docs/previews and update docs/visual/index.md for the new visual - 2026-02-23 10:21:49

Author: mgarcia01752