Public engineering-rule API

This release intentionally contains no normative machine-limit database.
Import MachineContext, Measurement, Rule, evaluate, IsoStage or measure_waveform
from vibration.iso. available_standards() is empty. select_rule() requests a
lawful external rule provider rather than recreating a standard's table.

Pass custom_rule=your_rule to evaluate. The caller owns applicability review,
rights, edition selection, threshold sourcing and machine/measurement coverage.
The software checks units, statistic, frame, band, duration and declared
qualification; no result is whole-machine compliance or an automatic trip.

See docs/USER_GUIDE.md for invented-number examples. Historical private ISO
test counts in old reports are not tests of this public replacement route.
