feat: ui rework and gear generator

lib/model/gear_ratio_codec.dart

@@ -0,0 +1,31 @@
+const double gearRatioMin = 0.25;
+const double gearRatioMax = 5.75;
+const int gearRatioEmptyRaw = 0;
+const int gearRatioMinRaw = 1;
+const int gearRatioMaxRaw = 255;
+
+const double gearRatioStep =
+    (gearRatioMax - gearRatioMin) / (gearRatioMaxRaw - gearRatioMinRaw);
+
+int encodeGearRatioByte(double value) {
+  if (value <= 0) {
+    return gearRatioEmptyRaw;
+  }
+  final clamped = value.clamp(gearRatioMin, gearRatioMax);
+  final scaled = ((clamped - gearRatioMin) / gearRatioStep).round();
+  return (gearRatioMinRaw + scaled)
+      .clamp(gearRatioMinRaw, gearRatioMaxRaw)
+      .toInt();
+}
+
+double decodeGearRatioByte(int raw) {
+  if (raw <= gearRatioEmptyRaw) {
+    return 0;
+  }
+  final clamped = raw.clamp(gearRatioMinRaw, gearRatioMaxRaw).toInt();
+  return gearRatioMin + (clamped - gearRatioMinRaw) * gearRatioStep;
+}
+
+double quantizeGearRatio(double value) {
+  return decodeGearRatioByte(encodeGearRatioByte(value));
+}