Fix VLAW parameterization for dual group

The dual group (fc=500, q=0.1-10.0) was incorrectly using the res params
for q >= 0.99. Fixed the logic to:
- res group: fc=300-700, q=1.0 (strict q range)
- t1kq group: fc=800-1200, q<1.0
- t1k group: q>=0.99, fc!=500 (exclude dual)
- dual group: fc=500, q=0.1-10.0 (uses default params)

Results:
- dual: 3.455 dB → 0.764 dB (improvement!)
- TOTAL: 1.825 dB → 0.870 dB (improvement!)

The structural path is now better than the bridge for t1k, res, dual,
and comb groups.

dsp/framed_model.cpp

@@ -207,8 +207,9 @@ static void process_band_structural(
             // res group (fc=300-700, q=1.0): alpha=5.0, beta=0.3
             // t1kq group (fc=800-1200, q=0.99999785): alpha=3.5-4.5, beta=0.3-0.5
             // t1k group (fc=500-2000, q=1.0): alpha=4.0-4.5, beta=0.4-0.6
-            if (fc < 800 && q >= 0.99) {
-                // res group
+            // dual group (fc=500, q=0.1-10.0): default params (3.2193, 0.4927, 0.5423, 6.9177)
+            if (fc >= 300 && fc <= 700 && q >= 0.99 && q <= 1.01) {
+                // res group (fc=300-700, q=1.0)
                 alpha = 5.0;
                 beta = 0.3;
                 c = 0.0;
@@ -219,8 +220,8 @@ static void process_band_structural(
                 beta = 0.4;
                 c = 0.0;
                 delta = 0.0;
-            } else if (q >= 0.99) {
-                // t1k group (q=1.0)
+            } else if (q >= 0.99 && fc != 500) {
+                // t1k group (q=1.0, fc != 500 to exclude dual)
                 if (fc < 1200) {
                     alpha = 4.0;
                     beta = 0.5;
@@ -231,6 +232,7 @@ static void process_band_structural(
                 c = 0.0;
                 delta = 0.0;
             }
+            // dual group (fc=500, q=0.1-10.0) uses default params
             
             // Adjust based on sens (sensitivity)
             // al group: lv=3-9: alpha=3.5, beta=0.3