feat(ai-ux): deduplicate AI queries, handle ServiceUnavailable retries, and optimize reader canvas graph prerendering (#44)

This Pull Request encapsulates all outstanding AI, Blazor InteractiveAuto lifecycle, pgvector, and Firefox authorization/session compatibility fixes.

### Key Accomplishments:
1. **Concurrent Request Deduplication (Option B):** Implemented a thread-safe active task registry in `KnowledgeService` that groups concurrent graph extraction queries for the same content, preventing duplicate AI calls completely.
2. **Resilience Strategy for Downstream Demands:** Extended the `ai-retry` resilience pipeline to automatically intercept and retry on temporary Google API `503 ServiceUnavailable` / `high demand` spikes.
3. **Interactive Graph Generation Guard (Option A):** Prevented server-side prerender-phase graph requests in the reader canvas component.
4. **Firefox Compatibility & Cookie Handler:** Implemented an authentication endpoint and hybrid hidden-form submission flow to solve login, registration, and logout redirections and cookies securely.
5. **Autoscrolling & Graph Exclusions:** Added concept-to-block smooth scrolling, active block badging, and filtered out markdown code blocks from being extracted as nodes.

All unit tests compiled and passed 100% cleanly.

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #44
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

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

@@ -1,4 +1,5 @@
 @page "/reader"
+@page "/reader/{BookId:guid}"
 @layout ReaderLayout
 @attribute [Authorize]
 @using NexusReader.UI.Shared.Services
@@ -8,6 +9,7 @@
 @inject IJSRuntime JS
 @inject NavigationManager NavManager
 @inject IReaderNavigationService NavService
+@inject IIdentityService IdentityService
 <PageTitle>Nexus E-Reader</PageTitle>
 
 <div class="home-reader-container">
@@ -16,6 +18,8 @@
 
 
 @code {
+    [Parameter] public Guid? BookId { get; set; }
+
     private ReaderCanvas? readerCanvas;
     private string? _activeQuizBlockId;
     
@@ -28,14 +32,31 @@
         QuizState.OnQuizRequested += HandleQuizRequestedAsync;
         FocusMode.OnFocusModeChanged += HandleUpdate;
         await FocusMode.InitializeAsync();
+    }
 
-        // Handle deep-linking to a specific chapter
+    protected override async Task OnParametersSetAsync()
+    {
         var uri = NavManager.ToAbsoluteUri(NavManager.Uri);
+        int chapterIndex = 0;
         if (Microsoft.AspNetCore.WebUtilities.QueryHelpers.ParseQuery(uri.Query).TryGetValue("chapter", out var chapterValue))
         {
-            if (int.TryParse(chapterValue, out var chapterIndex))
+            int.TryParse(chapterValue, out chapterIndex);
+        }
+
+        if (BookId.HasValue && BookId.Value != Guid.Empty)
+        {
+            if (NavService.CurrentEbookId != BookId.Value || NavService.CurrentChapterIndex != chapterIndex)
             {
-                await NavService.GoToChapter(chapterIndex);
+                NavService.SetBook(BookId.Value, chapterIndex);
+            }
+        }
+        else if (NavService.CurrentEbookId == Guid.Empty)
+        {
+            // If no BookId in URL and no book currently selected, try to load last read book
+            var profileResult = await IdentityService.GetProfileAsync();
+            if (profileResult.IsSuccess && profileResult.Value.LastReadBook != null)
+            {
+                NavService.SetBook(profileResult.Value.LastReadBook.Id, chapterIndex > 0 ? chapterIndex : profileResult.Value.LastReadBook.LastChapterIndex);
             }
         }
     }