fix: corpus 24-bit loader + LUT calibration env var

- Fix reshape error in corpus.py 24-bit WAV loader (misaligned data)
- Add RT_LUT_CAL env var for LUT output calibration
- Corpus results: TOTAL 2.397 (bridge 1.594), comb improved (-4.032)
- Structural chain regresses on t1kq/t1k/al/dual due to LUT curve mismatch
- The LUT produces different frequency response than plugin's FIR construction

dsp/framed_model.cpp

@@ -152,6 +152,10 @@ static void process_band_structural(
             double t = (dB - LUT_A) / (LUT_B - LUT_A);
             t = std::min(std::max(t, 0.0), 1.0);
             lvl = std::pow(t, static_cast<double>(LUT_GAMMA)) * LUT_MULT;
+            // RT_LUT_CAL: calibration multiplier on LUT output (empirical,
+            // calibrated against plugin steady-state mask@43=0.510).
+            static const double lut_cal = getenv("RT_LUT_CAL") ? atof(getenv("RT_LUT_CAL")) : 1.0;
+            lvl *= lut_cal;
         }
         band_level[k] = static_cast<float>(lvl);
     }