Checklist

• I have used the search function for OPEN ISSUES to see if someone else has already submitted the same feature request.

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Feature or improvement you want

Expose offline maps + support loading external map files for Android phones.

1 - Offline maps were implemented in PR #391 (March 2022), but the feature is hidden behind a dev flag and not accessible to regular users.
2 - Additionally, there is no way to load pre-downloaded map files (like MBTiles) from phone storage.

Solution:

1. Expose the existing offline maps download feature in the UI settings
2. Add ability to import external map tile files (MBTiles format)
   from device storage, similar to how device-ui supports offline
   maps on T-Deck via SD card

Why should this be added?

This would allow everyone to prepare map files and distribute
them to all team members before a trekking or in case of an emergency.

Use case:

• Trekking in remote area
• Emergency response and tactical operations without internet
• SAR (Search and Rescue) teams in remote areas

Screenshots / Drawings / Technical details

No response