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.Web/Program.cs

@@ -6,6 +6,7 @@ using NexusReader.Infrastructure;
 using NexusReader.Application.Abstractions.Services;
 using NexusReader.Application.Queries.User;
 using NexusReader.Application.Commands.Library;
+using NexusReader.Application.Queries.Library;
 using MediatR;
 using NexusReader.Web.Client.Services;
 using NexusReader.UI.Shared.Services;
@@ -235,6 +236,7 @@ if (!app.Environment.IsDevelopment())
     app.UseHttpsRedirection();
 }
 
+app.UseRouting();
 app.UseAuthentication();
 app.UseAuthorization();
 app.UseAntiforgery();
@@ -253,7 +255,9 @@ app.MapGet("/api/epub/{ebookId:guid}/{index:int}", async (Guid ebookId, int inde
     return Results.BadRequest(errorMsg);
 }).RequireAuthorization();
 
-var knowledgeApi = app.MapGroup("/api/knowledge").RequireAuthorization("HasAvailableTokens");
+var knowledgeApi = app.MapGroup("/api/knowledge")
+    .RequireAuthorization("HasAvailableTokens")
+    .DisableAntiforgery();
 
 knowledgeApi.MapPost("/", async (KnowledgeRequest request, ClaimsPrincipal user, IKnowledgeService knowledgeService) =>
 {
@@ -319,6 +323,7 @@ app.MapPost("/api/library/ingest", async ([FromBody] IngestEbookRequest request,
         request.AuthorName,
         coverData,
         epubData,
+        request.Description,
         userId
     );
 
@@ -328,6 +333,18 @@ app.MapPost("/api/library/ingest", async ([FromBody] IngestEbookRequest request,
     return Results.BadRequest(result.Errors.FirstOrDefault()?.Message ?? "Ingestion failed");
 }).RequireAuthorization().DisableAntiforgery();
 
+app.MapGet("/api/library/books", async (ClaimsPrincipal user, IMediator mediator) =>
+{
+    var userId = user.FindFirstValue(ClaimTypes.NameIdentifier);
+    if (string.IsNullOrEmpty(userId)) return Results.Unauthorized();
+
+    var result = await mediator.Send(new GetMyEbooksQuery(userId));
+    if (result.IsSuccess) return Results.Ok(result.Value);
+
+    var errorMsg = result.Errors.Count > 0 ? result.Errors[0].Message : "Unknown server error";
+    return Results.BadRequest(errorMsg);
+}).RequireAuthorization();
+
 app.MapPost("/api/StripeWebhook", async (
     HttpContext context, 
     UserManager<NexusUser> userManager, 
@@ -369,7 +386,7 @@ app.MapPost("/api/StripeWebhook", async (
     {
         return Results.BadRequest(e.Message);
     }
-});
+}).DisableAntiforgery();
 
 async Task HandleSubscriptionSuccess(
     string? email,