feat(01-input-ux-01): add WeightInput, RepsInput wrappers + stepper CSS

- WeightInput: wraps StepperInput with step=2.5, suffix=kg
- RepsInput: wraps StepperInput with step=1, no suffix
- App.css: appended stepper styles (.stepper-wrapper, .stepper-btn, etc.)
- Buttons min 44x44px touch targets, font-size 16px on input
- No existing CSS removed; block appended at end

frontend/src/components/RepsInput.jsx

@@ -0,0 +1,18 @@
+import StepperInput from './StepperInput';
+
+function RepsInput({ value, onChange, disabled = false }) {
+  return (
+    <StepperInput
+      value={value}
+      onChange={onChange}
+      step={1}
+      min={0}
+      max={null}
+      label="Reps"
+      suffix=""
+      disabled={disabled}
+    />
+  );
+}
+
+export default RepsInput;

frontend/src/components/WeightInput.jsx

@@ -0,0 +1,18 @@
+import StepperInput from './StepperInput';
+
+function WeightInput({ value, onChange, disabled = false }) {
+  return (
+    <StepperInput
+      value={value}
+      onChange={onChange}
+      step={2.5}
+      min={0}
+      max={null}
+      label="Weight"
+      suffix="kg"
+      disabled={disabled}
+    />
+  );
+}
+
+export default WeightInput;