feat(ui): Hub Navigation, Profile Dashboard and Auth Stability Fixes (#31)

This PR implements the Hub Navigation system and the Profile Dashboard, while resolving critical session synchronization issues.

### Key Changes
- **Hub Navigation**: Introduced `MainHubLayout` with a premium glassmorphism sidebar, providing access to Dashboard, Library, Concepts Map, and Profile.
- **Profile Dashboard**: Implemented a high-fidelity Profile page (#27) with learning metrics, AI token usage tracking, and system rank visualization.
- **Stability Fixes**:
    - Resolved an infinite network loop on the `/profile` page by implementing request deduplication and in-memory caching in `IdentityService`.
    - Added environment-aware guards to prevent illegal JavaScript interop calls during server-side prerendering.
    - Implemented automatic session invalidation on `401 Unauthorized` responses to handle stale authentication states gracefully.
- **Reader Integration**: Added a "Return to Dashboard" option in the reader toolbar (#26).

Closes #26
Closes #27

Reviewed-on: #31
Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Co-committed-by: Marek Jasiński <jasins.marek@gmail.com>

src/NexusReader.Application/Abstractions/Services/IEpubService.cs

@@ -5,5 +5,5 @@ namespace NexusReader.Application.Abstractions.Services;
 
 public interface IEpubService
 {
-    Task<Result<ReaderPageViewModel>> GetEpubContentAsync(int chapterIndex);
+    Task<Result<ReaderPageViewModel>> GetEpubContentAsync(int chapterIndex, string? userId = null);
 }

src/NexusReader.Application/Commands/Sync/UpdateReadingProgressCommand.cs

@@ -3,4 +3,11 @@ using MediatR;
 
 namespace NexusReader.Application.Commands.Sync;
 
-public record UpdateReadingProgressCommand(string PageId, string UserId, string? ExcludedConnectionId = null) : IRequest<Result>;
+public record UpdateReadingProgressCommand(
+    string PageId, 
+    string UserId, 
+    Guid EbookId, 
+    double Progress, 
+    string? ChapterTitle,
+    int ChapterIndex,
+    string? ExcludedConnectionId = null) : IRequest<Result>;

src/NexusReader.Application/DTOs/User/AuthorDto.cs

@@ -0,0 +1,7 @@
+namespace NexusReader.Application.DTOs.User;
+
+public record AuthorDto
+{
+    public int Id { get; init; }
+    public string Name { get; init; } = string.Empty;
+}

src/NexusReader.Application/DTOs/User/UserProfileDto.cs

@@ -4,6 +4,7 @@ public record UserProfileDto
 {
     public string Email { get; init; } = string.Empty;
     public int AITokensUsed { get; init; }
+    public Guid TenantId { get; init; }
     
     /// <summary>
     /// Relational data for the current subscription plan.
@@ -22,4 +23,9 @@ public record LastReadBookDto
 {
     public Guid Id { get; init; }
     public string Title { get; init; } = string.Empty;
+    public AuthorDto Author { get; init; } = new();
+    public string? CoverUrl { get; init; }
+    public double Progress { get; init; }
+    public string? LastChapter { get; init; }
+    public int LastChapterIndex { get; init; }
 }

src/NexusReader.Application/Queries/Reader/GetReaderPageQuery.cs

@@ -2,4 +2,4 @@ using NexusReader.Application.Abstractions.Messaging;
 
 namespace NexusReader.Application.Queries.Reader;
 
-public record GetReaderPageQuery(int ChapterIndex = 0) : IQuery<ReaderPageViewModel>;
+public record GetReaderPageQuery(int ChapterIndex = 0, string? UserId = null) : IQuery<ReaderPageViewModel>;

src/NexusReader.Application/Queries/Reader/GetReaderPageQueryHandler.cs

@@ -15,6 +15,6 @@ internal sealed class GetReaderPageQueryHandler : IQueryHandler<GetReaderPageQue
 
     public async Task<Result<ReaderPageViewModel>> Handle(GetReaderPageQuery request, CancellationToken cancellationToken)
     {
-        return await _epubService.GetEpubContentAsync(request.ChapterIndex);
+        return await _epubService.GetEpubContentAsync(request.ChapterIndex, request.UserId);
     }
 }

src/NexusReader.Application/Queries/Reader/ViewModels.cs

@@ -8,4 +8,4 @@ public abstract record ContentBlock(string Id);
 public record TextSegmentBlock(string Id, string Content) : ContentBlock(Id);
 public record AiActionTriggerBlock(string Id, string Dialogue, List<string> ActionOptions) : ContentBlock(Id);
 
-public record ReaderPageViewModel(List<ContentBlock> Blocks, int CurrentChapterIndex, int TotalChapters, string ChapterTitle);
+public record ReaderPageViewModel(List<ContentBlock> Blocks, int CurrentChapterIndex, int TotalChapters, string ChapterTitle, Guid EbookId = default);

src/NexusReader.Application/Queries/User/GetUserProfileQuery.cs

@@ -0,0 +1,7 @@
+using MediatR;
+using FluentResults;
+using NexusReader.Application.DTOs.User;
+
+namespace NexusReader.Application.Queries.User;
+
+public record GetUserProfileQuery(string UserId) : IRequest<Result<UserProfileDto>>;

src/NexusReader.Application/Queries/User/GetUserProfileQueryHandler.cs

@@ -0,0 +1,62 @@
+using MediatR;
+using FluentResults;
+using Microsoft.EntityFrameworkCore;
+using NexusReader.Application.DTOs.User;
+using NexusReader.Data.Persistence;
+
+namespace NexusReader.Application.Queries.User;
+
+public class GetUserProfileQueryHandler : IRequestHandler<GetUserProfileQuery, Result<UserProfileDto>>
+{
+    private readonly IDbContextFactory<AppDbContext> _dbContextFactory;
+
+    public GetUserProfileQueryHandler(IDbContextFactory<AppDbContext> dbContextFactory)
+    {
+        _dbContextFactory = dbContextFactory;
+    }
+
+    public async Task<Result<UserProfileDto>> Handle(GetUserProfileQuery request, CancellationToken cancellationToken)
+    {
+        using var dbContext = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
+        var profile = await dbContext.Users
+            .Where(u => u.Id == request.UserId)
+            .Select(u => new UserProfileDto
+            {
+                Email = u.Email ?? string.Empty,
+                AITokensUsed = u.AITokensUsed,
+                TenantId = u.TenantId != null && u.TenantId.Length == 36 ? new Guid(u.TenantId) : Guid.Empty,
+                Plan = u.SubscriptionPlan != null ? new SubscriptionPlanDto
+                {
+                    Id = u.SubscriptionPlan.Id,
+                    Name = u.SubscriptionPlan.PlanName,
+                    AITokenLimit = u.SubscriptionPlan.AITokenLimit,
+                    MonthlyPrice = u.SubscriptionPlan.MonthlyPrice
+                } : new SubscriptionPlanDto(),
+                AverageQuizScore = u.QuizResults.Any(q => q.TotalQuestions > 0) 
+                    ? (int)u.QuizResults.Where(q => q.TotalQuestions > 0).Average(q => (double)q.Score / q.TotalQuestions * 100) 
+                    : 0,
+                LastReadBook = u.Ebooks.OrderByDescending(e => e.LastReadDate).Select(e => new LastReadBookDto
+                {
+                    Id = e.Id,
+                    Title = e.Title,
+                    Author = new AuthorDto 
+                    { 
+                        Id = e.Author.Id, 
+                        Name = e.Author.Name 
+                    },
+                    CoverUrl = e.CoverUrl,
+                    Progress = e.Progress,
+                    LastChapter = e.LastChapter ?? "Rozpoczynanie...",
+                    LastChapterIndex = e.LastChapterIndex
+                }).FirstOrDefault()
+            })
+            .FirstOrDefaultAsync(cancellationToken);
+
+        if (profile == null)
+        {
+            return Result.Fail("Profile not found.");
+        }
+
+        return Result.Ok(profile);
+    }
+}