VAR Select Week Component

### VAR Select Week Component

Figma: [VAR Select Week](https://www.figma.com/design/WADcmVjJh5ARVoZ09xlpfdFN/DemocracyLab?node-id=39337-89483&t=2mfsTMQ1bhMOILO0-4)

### Location
**Component File:**

common/components/componentsBySection/VolunteerActivityReporting/VARSelectWeek.jsx

**Storybook File:**

common/components/componentsBySection/VolunteerActivityReporting/stories/VARSelectWeek.stories.jsx

**Styles File:**

civictechprojects/static/css/partials/_VARSelectWeek.scss

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**Props**
selectedWeek(string): Current week selected by the user from dropdown menu.
onUpdate(function): Callback function triggered when the user selects a new week. Passes the new week value back to the parent to update state.
errorMessage(string): Optional error message displayed below the dropdown. If empty, no error is shown.

**Test cases in Storybook**

- Default State: Renders heading, dropdown menu with default caption, and instructions
- Week Options: Renders all valid week ranges in dropdown menu
- Selected Week: Renders heading, dropdown menu with selected week, and instructions
- Error State: Renders heading, dropdown menu (with red border) with selected week, and error message in red.
- Responsive Design: ~~Confirm mobile/desktop resizes correctly.~~ Responsive rendering will be handled by container div

Start with common/components/componentsBySection/VolunteerActivityReporting/VARSelectWeek.jsx and its Storybook file, then compare the component with the linked Figma design and review civictechprojects/static/css/partials/_VARSelectWeek.scss. Use the Storybook test cases as the checklist: default, week options, selected week, and error states should render with the documented props and styling.

Written by the indexing model from the issue text.