feat(ui): implement hub navigation, profile dashboard and fix auth sync loop

- Added MainHubLayout with glassmorphism sidebar
- Implemented Profile dashboard with learn metrics
- Added request deduplication and caching to IdentityService
- Fixed infinite redirect loop on /profile page
- Added dashboard navigation from reader
- Closes #26, Closes #27

src/NexusReader.UI.Shared/Pages/Home.razor

@@ -1,4 +1,5 @@
-@page "/"
+@page "/reader"
+@layout ReaderLayout
 @attribute [Authorize]
 @using NexusReader.UI.Shared.Services
 @implements IAsyncDisposable