Add function to read positive number draft

src/app/App.tsx

@@ -200,6 +200,16 @@ function readNonNegativeNumberDraft(source: string, label: string): number {
   return value;
 }
 
+function readPositiveNumberDraft(source: string, label: string): number {
+  const value = Number(source);
+
+  if (!Number.isFinite(value) || value <= 0) {
+    throw new Error(`${label} must be a finite number greater than zero.`);
+  }
+
+  return value;
+}
+
 function areVec2Equal(left: Vec2, right: Vec2): boolean {
   return left.x === right.x && left.y === right.y;
 }