fix(draw_kit): reclaim 4x waveform oversample; relocate waveformColumnCount to component_geometry

kWaveformOversample set to 1 (was 4) — overbinning produced byte-identical pixels because columnMinMax exact partition already makes the draw gap-free. Comments credit columnMinMax, not oversampling.

tests/test_component_geometry.cpp

@@ -173,6 +173,22 @@ static void testListRowLayoutHitAgreement() {
     }
 }
 
+// --- waveformColumnCount -----------------------------------------------------
+
+static void testWaveformColumnCount() {
+    // Normal box: width minus the two 2px side insets.
+    CHECK(waveformColumnCount(KitBox{0, 0, 100, 40}) == 96);
+    CHECK(waveformColumnCount(KitBox{10, 5, 50, 20}) == 46);
+    // Minimum: a 5-wide box yields exactly 1 drawable column.
+    CHECK(waveformColumnCount(KitBox{0, 0, 5, 10}) == 1);
+    // Too narrow to have any drawable columns: 4 or fewer columns returns 0.
+    CHECK(waveformColumnCount(KitBox{0, 0, 4, 10}) == 0);
+    CHECK(waveformColumnCount(KitBox{0, 0, 1, 10}) == 0);
+    // Degenerate (empty) box returns 0 — graceful suppression.
+    CHECK(waveformColumnCount(KitBox{}) == 0);
+    CHECK(waveformColumnCount(KitBox{0, 0, 0, 40}) == 0);
+}
+
 int main() {
     testHitTestBoxHalfOpen();
     testButtonBoxInset();
@@ -190,6 +206,7 @@ int main() {
     testListRowHitTest();
     testListRowHitTestBoundedByCount();
     testListRowLayoutHitAgreement();
+    testWaveformColumnCount();
 
     if (g_fail == 0) std::printf("component_geometry: all tests passed\n");
     else std::printf("component_geometry: %d CHECK(s) FAILED\n", g_fail);