P4: METRIC FIX + log-domain LUT chain ported — honest baseline err <0.7 dB

Crucial: earlier dual ref -53.7 dB was a 24-bit-misdecoded artifact; honest ref is
-10.2 dB flat. Root cause of the "dual paradox" was a metric bug + missing log-domain
LUT. Ported the documented bridge (NOTES:147) into framed_model.cpp:
  xv=log10(am/res); C=G*LUT(xv)+W*warp^A; gain=(1-C)*res^rp.
Results (honest 24-bit metric): dual (fc=500 q-sweep) err <=0.7, t1kq fc-scan
err <=0.59. All empiric numbers explicitly marked. Structural A/B/gamma + combine/
FFT-conv still pending.

handoff/NOTES_LEVEL.md

@@ -948,3 +948,7 @@ VALIDATION (scale sweep):
    dB-domain LUT FIX_180563a60 (level_dB = 20·log10(mask) → t=(dB−A)/(B−A) clamp →
    t^γ), which COMPRESSES the exp2 collapse into a smooth log curve. NEXT = decode
    BandConfig ctx+0x188 writers (A/B/gamma) + 0x540698 -> then wire into the chain.
+
+## ============ UPDATE 2026-08-20q: METRIC FIX + LOG-DOMAIN LUT PORTED (honest baseline) ============
+### CRITICAL METRIC BUG FOUND: 24-bit refs mis-decoded as 16-bit
+Earlier dual