Add device settings management and web panel sync API

Features:
- New DeviceSettings admin page at /devicesettings
- Manage device server configurations (URL, mode, deviceId)
- 3 new API endpoints for APK sync functionality
- UserSettings database model with SQLite storage

Implementation:
- ServerSettingsController.cs with getUserSettings, updateUserSettings, getAllUserSettings
- DeviceSettings.cshtml Razor page with add/edit/delete UI
- DeviceSettings.cshtml.cs page model with CRUD operations
- UserSettings model added to ApiModels.cs
- UserSettings DbSet added to RR3DbContext
- EF Core migration: 20260219180936_AddUserSettings
- Link added to Admin dashboard

API Endpoints:
- GET /api/settings/getUserSettings?deviceId={id} - APK sync endpoint
- POST /api/settings/updateUserSettings - Web panel update
- GET /api/settings/getAllUserSettings - Admin list view

Database Schema:
- UserSettings table (Id, DeviceId, ServerUrl, Mode, LastUpdated)
- SQLite storage with EF Core migrations

Integration:
- Works with APK SettingsActivity sync button
- Real-time configuration updates
- Emoji logging for all operations
- Device-specific server URL management

Usage:
1. Admin configures device settings at /devicesettings
2. User opens RR3 APK and taps Sync from Web Panel
3. APK downloads settings via API
4. Settings saved to SharedPreferences
5. Game restart applies configuration

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

RR3CommunityServer/Models/ApiModels.cs

@@ -1,5 +1,15 @@
 namespace RR3CommunityServer.Models;
 
+// User Settings for Server Configuration
+public class UserSettings
+{
+    public int Id { get; set; }
+    public string DeviceId { get; set; } = string.Empty;
+    public string ServerUrl { get; set; } = string.Empty;
+    public string Mode { get; set; } = "offline"; // "online" or "offline"
+    public DateTime LastUpdated { get; set; } = DateTime.UtcNow;
+}
+
 // Progression request/response models
 public class ProgressionUpdate
 {