fix: update preSelection when input changes for selectsRange

When using selectsRange with input field changes, the preSelection state
was not being updated. This caused inconsistent calendar viewport behavior
when closing and reopening the datepicker after changing dates via input
vs via calendar click.

The fix updates preSelection to the new startDate when processing input
changes for range selection, matching the behavior of calcInitialState.

Fixes #5916

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: martijnrusschen

src/index.tsx

@@ -725,6 +725,12 @@ export class DatePicker extends Component<DatePickerProps, DatePickerState> {
         return;
       }
 
+      // Update preSelection to keep calendar viewport consistent when reopening
+      // Use startDate for preSelection to match calcInitialState behavior
+      if (startDateNew) {
+        this.setState({ preSelection: startDateNew });
+      }
+
       this.props.onChange?.([startDateNew, endDateNew], event);
     } else {
       // not selectsRange

src/test/datepicker_test.test.tsx

@@ -2337,6 +2337,39 @@ describe("DatePicker", () => {
 
     expect(onChangeSpy.mock.calls.at(-1)[0]).toStrictEqual([null, null]);
   });
+  it("should update preSelection when input changes for selectsRange", () => {
+    let instance: DatePicker | null = null;
+    const onChangeSpy = jest.fn();
+
+    render(
+      <DatePicker
+        ref={(node) => {
+          instance = node;
+        }}
+        selectsRange
+        startDate={newDate("2024-01-15")}
+        endDate={newDate("2024-01-20")}
+        onChange={onChangeSpy}
+        dateFormat="MM/dd/yyyy"
+      />,
+    );
+    expect(instance).toBeTruthy();
+
+    // Get initial preSelection
+    const initialPreSelection = instance!.state.preSelection;
+
+    // Change the date via input
+    fireEvent.change(instance!.input!, {
+      target: {
+        value: "02/10/2024 - 02/15/2024",
+      },
+    });
+
+    // preSelection should be updated to the new start date
+    expect(instance!.state.preSelection).not.toEqual(initialPreSelection);
+    expect(instance!.state.preSelection?.getMonth()).toBe(1); // February (0-indexed)
+    expect(instance!.state.preSelection?.getDate()).toBe(10);
+  });
   it("should correctly update the input when the value prop changes", () => {
     let instance: DatePicker | null = null;
     const { rerender } = render(