Position tracking starts with disabled location permissions

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**Description**
Users can still start position tracking in the Mergin Maps app even when location permissions are disabled in the device system settings. The time counter for position tracking runs, but no GPS path is actually being tracked, which may confuse users.

**Environment**
Staging

**Application (+ app version, build, operating system)**
- Android app version: 2025.4.0
- Android version: Android 14
- iOS app version: 2025.4.0
- iOS version: iOS 18.5

**Steps to reproduce**
1. Disable location permissions for Mergin Maps app in device system settings
2. Open Mergin Maps app
3. Start position tracking
4. Observe the time counter and GPS path

**Actual results**
- Position tracking can be started despite location permissions being disabled
- Time counter runs normally
- No GPS path is recorded/displayed

**Expected results**
- App should prevent starting position tracking when location permissions are disabled
- Alternatively, app should prompt the user to enable location permissions
- User should receive clear feedback that position tracking cannot function without permissions

**Screenshots or logs**
No screenshots provided.

*Conclusion*
*Created by GitHub Copilot and supervised by a human test analyst.*

Begin by reproducing the position-tracking flow on Android 14 and iOS 18.5 with location permissions disabled, then trace where tracking starts and how permission state is handled. Done means tracking is blocked or the user is prompted with clear feedback, and no timer runs without a GPS path.

Written by the indexing model from the issue text.