Progress Overhaul + Profile Page and a LOT more! (#4262)

Co-authored-by: Amelia <77553571+Fesaa@users.noreply.github.com>
Co-authored-by: Robbie Davis <robbie@therobbiedavis.com>

API/Entities/User/ClientDevice.cs

@@ -0,0 +1,49 @@
+using System;
+using System.Collections.Generic;
+using API.Constants;
+using API.Entities.Progress;
+
+namespace API.Entities.User;
+#nullable enable
+
+public class ClientDevice
+{
+    public int Id { get; set; }
+    /// <summary>
+    /// Client-provided device identifier (from <see cref="Headers.ClientDeviceFingerprint"/> header)
+    /// Null for clients that don't send it (OPDS readers, etc.)
+    /// </summary>
+    public string? UiFingerprint { get; set; }
+
+    /// <summary>
+    /// Server-computed fingerprint for device matching
+    /// Hash of: ClientType + Platform + DeviceType + (Browser+BrowserVersion for web-app)
+    /// </summary>
+    public string DeviceFingerprint { get; set; } = string.Empty;
+
+    /// <summary>
+    /// User-friendly name, defaults to generated name like "Chrome on Windows"
+    /// </summary>
+    /// <remarks>Generated on first seen, user can customize after the fact</remarks>
+    public string FriendlyName { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Most recent stable ClientInfoData (excluding IP/timestamp changes)
+    /// </summary>
+    public ClientInfoData CurrentClientInfo { get; set; } = new();
+
+    public DateTime FirstSeenUtc { get; set; }
+    public DateTime LastSeenUtc { get; set; }
+
+    /// <summary>
+    /// Soft delete - removed devices stay in DB for history
+    /// </summary>
+    public bool IsActive { get; set; } = true;
+
+    // TODO: Put an optional string? for AppUserAuthKey used (it might change, so it should be last seen)
+
+    // Navigation properties
+    public int AppUserId { get; set; }
+    public virtual AppUser AppUser { get; set; } = null!;
+    public ICollection<ClientDeviceHistory> History { get; set; } = [];
+}