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/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; }
 }