Initial commit: FieldLogger MAUI app with Maglink BLE support

Added Maglink RTK GNSS receiver integration with correct BLE UUIDs and device name filtering (ML-* prefix).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

FieldLogger/ViewModels/SettingsViewModel.cs

@@ -0,0 +1,52 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using FieldLogger.Models;
+using FieldLogger.Services;
+
+namespace FieldLogger.ViewModels;
+
+public sealed partial class SettingsViewModel : ObservableObject
+{
+    private readonly DeviceConnectionManager _manager;
+    private readonly SettingsService _settings;
+
+    public DeviceConnectionManager Manager => _manager;
+
+    [ObservableProperty]
+    private string _mapsApiKey = "";
+
+    public string AppVersion => AppInfo.Current.VersionString;
+
+    public SettingsViewModel(DeviceConnectionManager manager, SettingsService settings)
+    {
+        _manager = manager;
+        _settings = settings;
+        MapsApiKey = settings.GoogleMapsApiKey;
+    }
+
+    partial void OnMapsApiKeyChanged(string value) => _settings.GoogleMapsApiKey = value.Trim();
+
+    [RelayCommand]
+    private Task ChangeLocatorAsync() => Shell.Current.GoToAsync($"devicescan?kind={DeviceKind.Locator}");
+
+    [RelayCommand]
+    private Task ChangeGpsAsync() => Shell.Current.GoToAsync($"devicescan?kind={DeviceKind.RtkGps}");
+
+    [RelayCommand]
+    private async Task ForgetLocatorAsync()
+    {
+        if (await ConfirmForgetAsync(_manager.LocatorName ?? "locating receiver"))
+            await _manager.ForgetDeviceAsync(DeviceKind.Locator);
+    }
+
+    [RelayCommand]
+    private async Task ForgetGpsAsync()
+    {
+        if (await ConfirmForgetAsync(_manager.GpsName ?? "RTK GPS receiver"))
+            await _manager.ForgetDeviceAsync(DeviceKind.RtkGps);
+    }
+
+    private static Task<bool> ConfirmForgetAsync(string name) =>
+        Shell.Current.DisplayAlert("Forget Device",
+            $"Forget \"{name}\"? The app will no longer auto-connect to it.", "Forget", "Cancel");
+}