feat(visual): standardize FBC spectrum view and fix chart resize loop

- redesign GetCapture-FBC with standardized header row, optional Capture Time pill, and Device Info table
- map FBC payload from analysis.signal_analysis and primative mac address with N/A-safe sysDescr handling
- add compact capture metadata pills (bins, bin width, window average points, channel power)
- keep spectrum chart behavior while improving labels/theme (MHz axis, dBmV titles, centered chart title)
- fix Postman Chart.js 2 canvas stretch/runaway resize by using a fixed-height chart container
- regenerate visual docs/previews for GetCapture-FBC - 2026-02-22 23:45:33

Author: mgarcia01752