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/Components/Organisms/ReaderCanvas.razor

@@ -67,6 +67,7 @@
     private bool _isJsInitialized;
     private ElementReference _containerRef;
     private bool _isInteractive;
+    private string? _currentActiveBlockId;
 
     protected override async Task OnInitializedAsync()
     {
@@ -143,6 +144,7 @@
     [JSInvokable]
     public async Task HandleBlockReached(string blockId, string content)
     {
+        _currentActiveBlockId = blockId;
         await Coordinator.OnBlockReachedAsync(blockId, content);
 
         if (ViewModel != null)
@@ -160,8 +162,15 @@
 
     private async Task HandleSyncProgressReceived(string blockId, DateTime timestamp)
     {
+        if (string.IsNullOrEmpty(blockId) || blockId == _currentActiveBlockId)
+        {
+            Logger.LogDebug("[Sync] Received progress {BlockId} is empty or matches active block. Ignoring scroll.", blockId);
+            return;
+        }
+
         Logger.LogInformation("[Sync] Received progress from another device: block {BlockId} at {Timestamp}", blockId, timestamp);
 
+        _currentActiveBlockId = blockId;
         await ScrollToNodeAsync(blockId);
         await InvokeAsync(StateHasChanged);
     }
@@ -211,6 +220,8 @@
 
     private async Task LoadChapterAsync(int index)
     {
+        await Coordinator.ClearAsync();
+        _isJsInitialized = false; // Reset JS initialization to re-bind the scroll observer to new DOM elements!
         _isLoadingChapter = true;
         StatusMessage = "Wczytywanie treści...";
         StateHasChanged();
@@ -247,6 +258,18 @@
 
         _isLoadingChapter = false;
         StateHasChanged();
+
+        if (result.IsSuccess && !string.IsNullOrEmpty(NavigationService.PendingScrollBlockId))
+        {
+            var targetBlockId = NavigationService.PendingScrollBlockId;
+            NavigationService.PendingScrollBlockId = null; // Clear it to prevent multiple scrolls
+            _currentActiveBlockId = targetBlockId;
+
+            // Give the browser slightly more than one frame to render the loaded blocks
+            await Task.Delay(150);
+            await ScrollToNodeAsync(targetBlockId);
+            await InteractionService.RequestHighlightBlock(targetBlockId);
+        }
     }
 
     public async Task ScrollToNodeAsync(string id)