Proposed. Defines the RangeObservation record, a warn-only check mode
against --node-positions with tolerances from MEASURED ESP32-S3 FTM
bench data, per-boot calibration, and a fill mode gated off until a
source shows MEASURED p90 link error <= 0.3 m (expected from UWB).
Records the FTM bias between responder starts plainly and parks FTM
for check mode, coarse gating and time sync rather than dropping it.
Links ADR-144, ADR-281, rufield ADR-261, #2109 and #2133.
Co-Authored-By: claude-flow <ruv@ruv.net>
