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.UI.Shared/Services/IReaderNavigationService.cs

@@ -6,6 +6,7 @@ public interface IReaderNavigationService
     int CurrentChapterIndex { get; }
     int TotalChapters { get; }
     string ChapterTitle { get; }
+    string? PendingScrollBlockId { get; set; }
 
     event Func<Task>? OnNavigationChanged;
 

src/NexusReader.UI.Shared/Services/ISyncService.cs

@@ -7,5 +7,6 @@ public interface ISyncService
     Task<Result> InitializeAsync();
     Task<Result> UpdateProgressAsync(string pageId, Guid ebookId, double progress, string? chapterTitle, int chapterIndex);
     event Func<string, DateTime, Task> OnProgressReceived;
+    event Func<string, double, Task>? OnIngestionProgressReceived;
     Task DisposeAsync();
 }

src/NexusReader.UI.Shared/Services/IdentityService.cs

@@ -249,6 +249,25 @@ public class IdentityService : IIdentityService
         }
     }
 
+    public void ClearCache()
+    {
+        _cachedProfile = null;
+        if (OnStateInvalidated != null)
+        {
+            _ = Task.Run(async () =>
+            {
+                try
+                {
+                    await OnStateInvalidated.Invoke();
+                }
+                catch
+                {
+                    // Ignore exceptions from event handlers
+                }
+            });
+        }
+    }
+
     private class LoginResponse
     {
         public string TokenType { get; set; } = string.Empty;

src/NexusReader.UI.Shared/Services/KnowledgeCoordinator.cs

@@ -17,6 +17,8 @@ public sealed partial class KnowledgeCoordinator : IDisposable
     private readonly IReaderInteractionService _interactionService;
     private readonly ILogger<KnowledgeCoordinator> _logger;
     
+    public string CurrentFullPageContent { get; private set; } = string.Empty;
+    
     /// <summary>
     /// Raised when the knowledge graph has been updated with new data.
     /// Subscribers must return a Task to enable proper async handling.
@@ -77,6 +79,7 @@ public sealed partial class KnowledgeCoordinator : IDisposable
     {
         if (string.IsNullOrWhiteSpace(fullContent)) return;
 
+        CurrentFullPageContent = fullContent;
         LogGeneratingGraph(tenantId);
         
         await _graphService.Clear();
@@ -94,11 +97,15 @@ public sealed partial class KnowledgeCoordinator : IDisposable
                     if (OnGraphUpdated != null)
                         await OnGraphUpdated.Invoke(packet.Graph);
                     await _platformService.VibrateSuccessAsync();
+                    return;
                 }
             }
+            
+            await _graphService.SetLoading(false);
         }
         catch (Exception ex)
         {
+            await _graphService.SetLoading(false);
             LogGraphError(ex, tenantId);
         }
     }
@@ -144,6 +151,7 @@ public sealed partial class KnowledgeCoordinator : IDisposable
 
     public async Task ClearAsync()
     {
+        CurrentFullPageContent = string.Empty;
         await _graphService.Clear();
         await _quizService.SetQuiz(null, null);
     }

src/NexusReader.UI.Shared/Services/ReaderNavigationService.cs

@@ -15,6 +15,7 @@ public class ReaderNavigationService : IReaderNavigationService
     public int CurrentChapterIndex { get; private set; } = 0;
     public int TotalChapters { get; private set; } = 1;
     public string ChapterTitle { get; private set; } = "Loading...";
+    public string? PendingScrollBlockId { get; set; }
 
     public event Func<Task>? OnNavigationChanged;
 

src/NexusReader.UI.Shared/Services/SyncService.cs

@@ -16,6 +16,7 @@ public class SyncService : ISyncService, IAsyncDisposable
     private CancellationTokenSource? _debounceCts;
 
     public event Func<string, DateTime, Task>? OnProgressReceived;
+    public event Func<string, double, Task>? OnIngestionProgressReceived;
 
     public SyncService(
         HttpClient httpClient,
@@ -50,9 +51,20 @@ public class SyncService : ISyncService, IAsyncDisposable
         _hubConnection.On<string, DateTime>("ProgressUpdated", async (pageId, timestamp) =>
         {
             // Note: In the future we might want to receive ebookId and progress here too
+            if (pageId == _lastSentPageId)
+            {
+                _logger.LogDebug("[Sync] Ignoring self progress update for page {PageId}.", pageId);
+                return;
+            }
+            _lastSentPageId = pageId; // Prevent echoing back duplicate progress updates
             if (OnProgressReceived != null) await OnProgressReceived(pageId, timestamp);
         });
 
+        _hubConnection.On<string, double>("IngestionProgress", async (message, progress) =>
+        {
+            if (OnIngestionProgressReceived != null) await OnIngestionProgressReceived(message, progress);
+        });
+
         try
         {
             await _hubConnection.StartAsync();
@@ -71,6 +83,8 @@ public class SyncService : ISyncService, IAsyncDisposable
     {
         if (pageId == _lastSentPageId) return Result.Ok();
         
+        _lastSentPageId = pageId;
+        
         // Proper trailing-edge debounce
         _debounceCts?.Cancel();
         _debounceCts = new CancellationTokenSource();
@@ -86,8 +100,7 @@ public class SyncService : ISyncService, IAsyncDisposable
 
                 if (_hubConnection?.State == HubConnectionState.Connected)
                 {
-                    await _hubConnection.SendAsync("UpdateProgress", pageId, ebookId, progress, chapterTitle, token);
-                    _lastSentPageId = pageId;
+                    await _hubConnection.SendAsync("UpdateProgress", pageId, ebookId, progress, chapterTitle, chapterIndex);
                 }
             }
             catch (TaskCanceledException) { /* Ignored, user kept scrolling */ }