spectral: vectors instead of new[]; vlaw: extract law + vlaw_check target

- spectral.cpp: window_/buf_/tmp_buf_/fir_buf_/fir_freq_ as std::vector (no
  exception-leak in ctor, destructor = default)
- framed_model.hpp: extract vlaw_cut/vlaw_mask inline (BLOCKMAP:314 softplus)
- dsp/vlaw_check.cpp: unit test for law (monotonic, zero-level, delta, ref,
  comb-neutral) — PASS
- CMake: add vlaw_check target
- Guard: corpus --compare d=+0.000, fn529fe0_check PASS, twin_check PASS

dsp/vlaw_check.cpp

@@ -0,0 +1,55 @@
+#include <cstdio>
+#include <cmath>
+#include "framed_model.hpp"
+
+// Unit check for the VLAW detector law (BLOCKMAP:314 softplus proxy):
+//   cut  = alpha * ln1p(lvl/beta) + c [+ delta]
+//   mask = 10^(-cut/20)
+// Reference values hand-computed from the dual-calibrated constants
+// (alpha=3.2193, beta=0.4927, c=0.5423, delta=6.9177 — README.md:26).
+int main() {
+    int fail = 0;
+
+    // --- law monotonicity: higher level -> stronger cut -> smaller mask ---
+    double m0 = vlaw_mask(0.01, 3.2193, 0.4927, 0.5423, 0.0);
+    double m1 = vlaw_mask(1.0,  3.2193, 0.4927, 0.5423, 0.0);
+    double m2 = vlaw_mask(10.0, 3.2193, 0.4927, 0.5423, 0.0);
+    bool mono = (m0 > m1) && (m1 > m2);
+    std::printf("vlaw monotonic: m(0.01)=%.4f m(1)=%.4f m(10)=%.4f (%s)\n",
+                m0, m1, m2, mono ? "OK" : "MISMATCH");
+    if (!mono) fail = 1;
+
+    // --- zero level: cut = c => mask = 10^(-c/20) ---
+    double mz = vlaw_mask(0.0, 3.2193, 0.4927, 0.5423, 0.0);
+    double ez = std::pow(10.0, -0.5423 / 20.0);
+    bool zok = std::fabs(mz - ez) < 1e-9;
+    std::printf("vlaw zero-level: mask=%.6f expect=%.6f (%s)\n",
+                mz, ez, zok ? "OK" : "MISMATCH");
+    if (!zok) fail = 1;
+
+    // --- delta branch adds cut -> deeper mask ---
+    double md = vlaw_mask(1.0, 3.2193, 0.4927, 0.5423, 6.9177);
+    bool dok = md < m1;
+    std::printf("vlaw delta: mask+delta=%.4f < %.4f (%s)\n",
+                md, m1, dok ? "OK" : "MISMATCH");
+    if (!dok) fail = 1;
+
+    // --- numeric reference: lvl=1.0, dual params ---
+    // cut = 3.2193 * ln(1 + 1/0.4927) + 0.5423
+    double cut_ref = 3.2193 * std::log1p(1.0 / 0.4927) + 0.5423;
+    double mref = std::pow(10.0, -cut_ref / 20.0);
+    bool rok = std::fabs(m1 - mref) < 1e-9;
+    std::printf("vlaw ref: mask=%.6f expect=%.6f cut=%.4f (%s)\n",
+                m1, mref, cut_ref, rok ? "OK" : "MISMATCH");
+    if (!rok) fail = 1;
+
+    // --- comb neutrality: alpha=0.05 beta=5.0 c=0 -> mask ~ 1 for lvl=0 ---
+    double mc = vlaw_mask(0.0, 0.05, 5.0, 0.0, 0.0);
+    bool cok = std::fabs(mc - 1.0) < 1e-9;
+    std::printf("vlaw comb-neutral: mask(0)=%.6f expect=1.0 (%s)\n",
+                mc, cok ? "OK" : "MISMATCH");
+    if (!cok) fail = 1;
+
+    std::printf("vlaw_check %s\n", fail ? "FAIL" : "PASS");
+    return fail;
+}