Date Picker Input Widget

[Allaoua9]

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This PR is related to https://github.com/Chainlit/chainlit/issues/2652

• Backend: new DatePicker widget class with mode, min/max, placeholder, and ISO validation, exposed via InputWidgetType.
• Frontend: DatePickerInput component (single + range) based on shadcn datepicker.
• i18n: locale-aware formatting via getDateFnsLocale plus placeholder strings in every translation file.
• Dependencies: add react-day-picker@^9.11.1 and date-fns@^4.1.0.

Single Date

Date Range :

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Summary by cubic

Added a DatePicker input widget for chat settings with single and range modes, min/max bounds, ISO-safe values, and locale-aware display.

• New Features

  • Backend: DatePicker widget with mode, initial/min/max, format, placeholder, ISO parsing/validation, and InputWidgetType "datepicker".
  • Frontend: DatePickerInput (single and range) with calendar UI, confirm/reset for ranges, disabled days from bounds, and integration in FormInput.
  • i18n: locale mapping via date-fns and placeholders across all translations.

• Dependencies

  • Added react-day-picker ^9.11.1 and date-fns ^4.1.0.

^{Written for commit 5fe341e14cf4021dc3a8f0ac1ce4a5ccda5060bc. Summary will update automatically on new commits.}