fix(docs): calendar hijri doc fixed to show correct months in dropdown layout

[sina-byn]

Fix Persian / Jalali Calendar Month Dropdown Display

This PR addresses the issue where the month dropdown in the Persian / Jalali calendar captionLayout='dropdown' was still displaying Gregorian months.

Fixes/Closes #8305

Changes include:

Updated the documentation/example to show how to pass the formatMonthDropdown function when instantiating the Calendar component:

<Calendar
  mode="single"
  selected={date}
  onSelect={handleDateSelect}
  autoFocus
  captionLayout="dropdown"
  formatters={{
    formatMonthDropdown: (date) =>
      date.toLocaleString("fa-IR", { month: "short" }),
  }}
/>;

Result:

• Month dropdown now correctly displays Persian / Jalali month names.
• Provides both instance-level and global ways to configure month formatting.

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