feat(date-picker): support configurable week starts

apps/docs/src/components/date-picker.stories.tsx

@@ -37,7 +37,7 @@ function DatePickerPlayground() {
 
 function DatePickerScenarios() {
   return (
-    <div className="grid w-full max-w-4xl gap-4 md:grid-cols-2">
+    <div className="grid w-full max-w-6xl gap-4 md:grid-cols-2 xl:grid-cols-3">
       <Card>
         <CardHeader>
           <CardTitle>Empty state</CardTitle>
@@ -48,6 +48,24 @@ function DatePickerScenarios() {
         </CardContent>
       </Card>
 
+      <Card>
+        <CardHeader>
+          <CardTitle>Sunday-first calendar</CardTitle>
+          <CardDescription>
+            Opt into Sunday-through-Saturday when matching US-style calendar conventions.
+          </CardDescription>
+        </CardHeader>
+        <CardContent>
+          <DatePicker
+            aria-label="Sunday-first launch date"
+            defaultMonth={new Date(2026, 2, 1)}
+            defaultValue={new Date(2026, 2, 18)}
+            locale="en-US"
+            weekStartsOn="sunday"
+          />
+        </CardContent>
+      </Card>
+
       <Card>
         <CardHeader>
           <CardTitle>Guardrailed window</CardTitle>
@@ -76,7 +94,7 @@ const meta = {
     docs: {
       description: {
         component:
-          "A single-date picker for launch windows, review deadlines, and operator scheduling surfaces. This first slice stays intentionally narrow: one date, one popover calendar, no range or timezone API."
+          "A single-date picker for launch windows, review deadlines, and operator scheduling surfaces. It defaults to a Monday-through-Sunday calendar, with an opt-in Sunday-first mode for teams that need that convention. This first slice stays intentionally narrow: one date, one popover calendar, no range or timezone API."
       }
     },
     layout: "centered"