feat(search/rag): implement NexusSearchBox, dynamic Qdrant collection auto-provisioning, batch vector ingestion, mobile Serilog logging, and resolve 401 auth handler error (#51)

Resolves #52

This Pull Request introduces the **NexusSearchBox** search feature with premium unified styling, implements a robust **dynamic Qdrant collection auto-provisioning and batch-vector ingestion pipeline**, integrates a unified **Serilog logging infrastructure** for the Blazor Hybrid environment (MAUI), and resolves the **401 Unauthorized API header propagation error** inside mobile builds.

### 🚀 Key Implementations

#### 1. Premium `NexusSearchBox` & Semantic Search UI
* **NexusSearchBox Component:** Created an elegant search-as-you-type search box with smooth key navigation, quick-clearing, and seamless dynamic styling.
* **Unified Aesthetics:** Refactored the search box isolated styling to align perfectly with the dashboard's design system using glassmorphism, `--nexus-neon` token gradients, and smooth pulse/fade animations.
* **Semantic Search Integration:** Integrated semantic search query dispatching (`SearchLibrarySemanticallyQuery`) and wired up navigation seamlessly through the updated `ReaderNavigationService`.
* **Tests Hardening:** Added/adapted query assertions in `QueryTests.cs` to guarantee safe parameterization and error boundary mapping.

#### 2. Qdrant Collection Provisioning & Vector Ingestion
* **Dynamic Auto-Provisioning:** Implemented dynamic checking and lazy-creation of the `knowledge_units` collection using 768 dimensions and Cosine distance.
* **High-Performance Ingestion:** Optimized `ProcessKnowledgeUnitsAsync` with high-performance batch embedding generation using `_embeddingGenerator` and deterministic MD5 GUIDs for stable, duplicate-free upsertion.
* **Database Cache Clear Sync:** Integrated Qdrant collection deletion in `ClearCacheAsync` to ensure absolute consistency between the PostgreSQL database cache and vector database indices.

#### 3. Cross-Platform MAUI Logging (Serilog Infrastructure)
* **Serilog Integration:** Configured cross-platform Serilog routing in `SerilogConfiguration.cs`, streaming diagnostic logs safely across native platforms and the Blazor Webview container.
* **Interop Bridge:** Built `BlazorLoggingBridge.cs` to capture web console messages and pipe them directly to the native host logger.
* **Demo Interface:** Added an interactive `SerilogDemo.razor` sandbox under Pages.

#### 4. Resolving 401 Load Errors (Authentication Handler Flow)
* **Authentication Header Handler:** Implemented the `MobileAuthenticationHeaderHandler` to correctly extract, validate, and inject bearer JWT tokens into outbound API requests.
* **Configuration-based API Host:** Structured standard API URI routing to use clean configuration bindings in `appsettings.json`.

---

### 🧪 Verification & Build Status
* Run `dotnet build` from the solution root: Successfully compiled the full multi-targeted solution (`Liczba błędów: 0`).
* All unit and integration tests successfully executed and verified (`dotnet test`).

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Co-authored-by: Marek Jaisński <jasins.marek@gmail.com>
Reviewed-on: #51
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

src/NexusReader.Web/Program.cs

@@ -106,7 +106,8 @@ builder.Services.AddAuthentication(options =>
 
 builder.Services.AddIdentityApiEndpoints<NexusUser>()
     .AddRoles<IdentityRole>()
-    .AddEntityFrameworkStores<AppDbContext>();
+    .AddEntityFrameworkStores<AppDbContext>()
+    .AddClaimsPrincipalFactory<NexusReader.Web.Services.CustomUserClaimsPrincipalFactory>();
 
 builder.Services.ConfigureApplicationCookie(options =>
 {
@@ -194,6 +195,7 @@ using (var scope = app.Services.CreateScope())
 
             await dbContext.Database.MigrateAsync();
             await DbInitializer.SeedAsync(services);
+            await TriggerBackgroundProcessingForUnindexedBooksAsync(services);
 
             if (logger.IsEnabled(LogLevel.Information))
             {
@@ -337,13 +339,16 @@ app.MapPost("/api/library/ingest", async ([FromBody] IngestEbookRequest request,
         ? Convert.FromBase64String(request.CoverImageBase64) 
         : null;
 
+    var tenantId = user.FindFirst("TenantId")?.Value ?? "global";
+
     var command = new IngestEbookCommand(
         request.Title,
         request.AuthorName,
         coverData,
         epubData,
         request.Description,
-        userId
+        userId,
+        tenantId
     );
 
     var result = await mediator.Send(command);
@@ -563,6 +568,50 @@ app.MapRazorComponents<App>()
 
 app.Run();
 
+async Task TriggerBackgroundProcessingForUnindexedBooksAsync(IServiceProvider services)
+{
+    var logger = services.GetRequiredService<ILogger<Program>>();
+    try
+    {
+        var dbContextFactory = services.GetRequiredService<IDbContextFactory<NexusReader.Data.Persistence.AppDbContext>>();
+        using var dbContext = await dbContextFactory.CreateDbContextAsync();
+        
+        var unindexedEbooks = await dbContext.Ebooks
+            .Where(e => !e.IsReadyForReading)
+            .ToListAsync();
+            
+        if (unindexedEbooks.Any())
+        {
+            logger.LogInformation("[Startup] Found {Count} un-indexed ebooks. Triggering background processing...", unindexedEbooks.Count);
+            
+            foreach (var ebook in unindexedEbooks)
+            {
+                logger.LogInformation("[Startup] Queuing background processing for ebook: '{Title}' ({Id})", ebook.Title, ebook.Id);
+                
+                _ = Task.Run(async () =>
+                {
+                    try
+                    {
+                        using var scope = services.CreateScope();
+                        var scopedMediator = scope.ServiceProvider.GetRequiredService<IMediator>();
+                        await scopedMediator.Send(new ProcessEbookCommand(ebook.Id, ebook.UserId, ebook.TenantId));
+                    }
+                    catch (Exception ex)
+                    {
+                        using var scope = services.CreateScope();
+                        var scopedLogger = scope.ServiceProvider.GetRequiredService<ILogger<Program>>();
+                        scopedLogger.LogError(ex, "Failed to run background processing for ebook {EbookId} on startup", ebook.Id);
+                    }
+                });
+            }
+        }
+    }
+    catch (Exception ex)
+    {
+        logger.LogError(ex, "Error checking or triggering background processing for unindexed books on startup.");
+    }
+}
+
 public record KnowledgeRequest(string Text, Guid? EbookId = null);
 public record GroundednessRequest(string Answer, string Context);
 public record SemanticSearchRequest(string QueryText, int Limit = 5);