Add AHU fault batch 6: FC-006/008/010/014/015 - AHU chapter complete (#12)

Final five rules verified against engine e2ff2f8. The AHU chapter now
stands at 31/31 faults verified, all scenarios green.

- AHU-FC-006 OA fraction deviation (G36 FC#6): FC-055's fraction core
  with a two-sided Abs test and the dTMIN evaluability conjunct both
  in-graph and exposed as yTempDeltaOk (it is part of G36's own
  equation). Cards document that the low-side ventilation branch is
  nearly unreachable at NISTIR defaults (damper fully shut gives
  |dev| = 0.15 vs the 0.30 band) - what it actually catches is a
  negative inferred fraction, a sensor/mixing contradiction. Also
  records an IEEE-754 non-representability artifact at the high
  tolerance boundary rather than hiding it.
- AHU-FC-008/010 approximate-equality pair: |SAT - dTSF - MAT| and
  |MAT - OAT| against root-sum-square sensor errors (sqrt(10) =
  3.1623), with worked retunes for global OAT sensors and different
  epsilons. FC-010's at-threshold vectors are ULP-exact by
  construction.
- AHU-FC-014/015 inactive-coil signatures (severity 2, CRITICAL_WASTE
  /HIGH/DIRECT per the 5.8.1 index): mat/sat bound as coil-temp
  proxies per G36's own note; the +dTSF fan-heat term worked through
  per fault (physically necessary for 015, doubly conservative for
  014, with retune arithmetic). Catches the leaking valve FC-050 is
  structurally blind to.

FC-062's suppresses list now carries its full contract: all eleven
MAT-consuming rules. Playbooks: economizer-failure += FC-006,
sensor-drift += FC-008/010 (stuck-actuator already listed 014/015).
README: all 31 rows verified.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: jscott3201