feat: Enhance map functionality with download area selection and user location pointer

- Added download area selection feature in MapProvider with methods to enter, exit, and update bounds.
- Implemented DownloadAreaOverlay widget for user interface during download area selection.
- Integrated download area preview in MapManagementScreen with visual feedback.
- Introduced LocationPointer widget to indicate user location and heading on the map.
- Updated localization strings in app_sl.arb for improved clarity and accuracy.
- Refactored map marker generation to utilize the new LocationPointer for user location representation.
- Improved error handling in LocationTrackingService for initial position setting.

lib/l10n/untranslated.json

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