fix: initialize ComboboxArea with default selected area

[fityannugroho]

Summary

This PR fixes the area selector behavior by passing the currently selected area into the Combobox on mount.

Changes

• components/ComboboxArea.tsx: add defaultSelected prop and initialize internal selectedArea state from it.
• modules/MapDashboard/AreaSelectors.tsx: pass selectedArea[area] as defaultSelected to ComboboxArea.

Why

Previously the combobox did not reflect the existing selection when the selector UI mounted. This ensures the UI shows the current selection immediately.

How to test

1. Open the map dashboard and verify the area comboboxes display the currently selected area.
2. Select a different area and ensure linked child selectors update.

Checklist:

• Pass current selected area to ComboboxArea
• Initialize ComboboxArea internal state from prop
• Verified changes are minimal and localized