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/Controllers/ServerSettingsController.cs

@@ -0,0 +1,174 @@
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.EntityFrameworkCore;
+using RR3CommunityServer.Data;
+using RR3CommunityServer.Models;
+
+namespace RR3CommunityServer.Controllers;
+
+[ApiController]
+[Route("api/settings")]
+public class ServerSettingsController : ControllerBase
+{
+    private readonly RR3DbContext _context;
+    private readonly ILogger<ServerSettingsController> _logger;
+
+    public ServerSettingsController(RR3DbContext context, ILogger<ServerSettingsController> logger)
+    {
+        _context = context;
+        _logger = logger;
+    }
+
+    /// <summary>
+    /// Get user settings (called by APK sync button)
+    /// GET /api/settings/getUserSettings?deviceId=xxx
+    /// </summary>
+    [HttpGet("getUserSettings")]
+    public async Task<ActionResult<UserSettingsResponse>> GetUserSettings([FromQuery] string? deviceId)
+    {
+        try
+        {
+            if (string.IsNullOrEmpty(deviceId))
+            {
+                _logger.LogWarning("GetUserSettings: No deviceId provided");
+                return BadRequest(new { error = "deviceId is required" });
+            }
+
+            _logger.LogInformation($"🔄 GetUserSettings: deviceId={deviceId}");
+
+            var settings = await _context.UserSettings
+                .Where(s => s.DeviceId == deviceId)
+                .FirstOrDefaultAsync();
+
+            if (settings == null)
+            {
+                _logger.LogInformation($"⚠️ No settings found for deviceId={deviceId}, returning defaults");
+                return Ok(new UserSettingsResponse
+                {
+                    mode = "offline",
+                    serverUrl = "",
+                    message = "No settings found, using defaults"
+                });
+            }
+
+            _logger.LogInformation($"✅ Found settings: mode={settings.Mode}, url={settings.ServerUrl}");
+            return Ok(new UserSettingsResponse
+            {
+                mode = settings.Mode,
+                serverUrl = settings.ServerUrl,
+                message = "Settings retrieved successfully"
+            });
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "❌ Error in GetUserSettings");
+            return StatusCode(500, new { error = "Internal server error" });
+        }
+    }
+
+    /// <summary>
+    /// Update user settings (called by web panel)
+    /// POST /api/settings/updateUserSettings
+    /// Body: { "deviceId": "xxx", "mode": "online", "serverUrl": "https://example.com:8443" }
+    /// </summary>
+    [HttpPost("updateUserSettings")]
+    public async Task<ActionResult<UpdateSettingsResponse>> UpdateUserSettings([FromBody] UpdateUserSettingsRequest request)
+    {
+        try
+        {
+            if (string.IsNullOrEmpty(request.deviceId))
+            {
+                return BadRequest(new { error = "deviceId is required" });
+            }
+
+            if (string.IsNullOrEmpty(request.mode))
+            {
+                return BadRequest(new { error = "mode is required" });
+            }
+
+            _logger.LogInformation($"🔄 UpdateUserSettings: deviceId={request.deviceId}, mode={request.mode}, url={request.serverUrl}");
+
+            var settings = await _context.UserSettings
+                .Where(s => s.DeviceId == request.deviceId)
+                .FirstOrDefaultAsync();
+
+            if (settings == null)
+            {
+                // Create new settings
+                settings = new UserSettings
+                {
+                    DeviceId = request.deviceId,
+                    Mode = request.mode,
+                    ServerUrl = request.serverUrl ?? "",
+                    LastUpdated = DateTime.UtcNow
+                };
+                _context.UserSettings.Add(settings);
+                _logger.LogInformation($"➕ Created new settings for deviceId={request.deviceId}");
+            }
+            else
+            {
+                // Update existing settings
+                settings.Mode = request.mode;
+                settings.ServerUrl = request.serverUrl ?? "";
+                settings.LastUpdated = DateTime.UtcNow;
+                _logger.LogInformation($"✏️ Updated existing settings for deviceId={request.deviceId}");
+            }
+
+            await _context.SaveChangesAsync();
+
+            return Ok(new UpdateSettingsResponse
+            {
+                success = true,
+                message = "Settings updated successfully"
+            });
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "❌ Error in UpdateUserSettings");
+            return StatusCode(500, new { error = "Internal server error" });
+        }
+    }
+
+    /// <summary>
+    /// Get all user settings (for admin panel)
+    /// GET /api/settings/getAllUserSettings
+    /// </summary>
+    [HttpGet("getAllUserSettings")]
+    public async Task<ActionResult<List<UserSettings>>> GetAllUserSettings()
+    {
+        try
+        {
+            var allSettings = await _context.UserSettings
+                .OrderByDescending(s => s.LastUpdated)
+                .ToListAsync();
+
+            _logger.LogInformation($"📋 Retrieved {allSettings.Count} user settings");
+            return Ok(allSettings);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "❌ Error in GetAllUserSettings");
+            return StatusCode(500, new { error = "Internal server error" });
+        }
+    }
+}
+
+// Response models
+public class UserSettingsResponse
+{
+    public string mode { get; set; } = "offline";
+    public string serverUrl { get; set; } = "";
+    public string? message { get; set; }
+}
+
+public class UpdateUserSettingsRequest
+{
+    public string deviceId { get; set; } = string.Empty;
+    public string mode { get; set; } = "offline";
+    public string? serverUrl { get; set; }
+}
+
+public class UpdateSettingsResponse
+{
+    public bool success { get; set; }
+    public string? message { get; set; }
+}