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/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);
     }