feat(rag): implement KM-RAG retrieval read-path, API endpoints, global Q&A UI, and unit tests (#49)

This Pull Request implements the complete **Retrieval module (Read Path)** for the Knowledge-Map RAG (KM-RAG) architecture within the NexusReader platform. It resolves all requirements for vector-based semantic search, Neo4j graph context expansion, structured grounding with Google Gemini, API/Wasm integration, and an interactive front-end global Q&A panel.

Resolves #48

### 🚀 Key Implementations

1. **Grounded DTOs & Schema Definition**
   - Added `GroundedResponseDto` and `CitationDto` for strict JSON Schema matching with Gemini.

2. **Core Service & Read Path Logic**
   - Implemented the robust **5-step pipeline** in `KnowledgeService.AskQuestionAsync`:
     1. *Embedding*: Query vectorization using `IEmbeddingGenerator`.
     2. *Semantic Search*: Multi-tenant vector search with Qdrant, supporting scoping to a specific book or global search.
     3. *Graph Expansion*: Fetching connected concepts and parent relationships using Neo4j Cypher.
     4. *Citation Hydration*: Cross-referencing results with PostgreSQL to fetch book titles and accurate chapter citations.
     5. *Grounded Generation*: Strict structured generation via `IChatClient` (Gemini) preventing hallucinations and using citations.

3. **CQRS & Endpoints**
   - Added `AskLibraryQuestionQuery` and its handler.
   - Mapped `/api/knowledge/ask` and `/api/knowledge/search` endpoints inside `Program.cs`.
   - Updated `WasmKnowledgeService` to support proxying retrieval requests.

4. **Premium Blazor UI Panel**
   - Implemented `/intelligence` (Global AI Q&A) with a curated HSL palette, dark theme, smooth micro-animations, loading shimmers, and side-by-side citation cards.
   - Registered the panel within the `MainHubLayout` sidebar.

5. **Test Coverage**
   - Wrote comprehensive xUnit tests in `QueryTests.cs` using Moq and FluentAssertions to assert that handlers correctly validate input and interact with services.

### 🧪 Verification
- Verified compilation and build gate successfully (`dotnet build`: 0 errors).
- All 7 tests passed perfectly (`dotnet test`).

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #49
Reviewed-by: Marek Jaisński <jasins.marek@gmail.com>
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

src/NexusReader.Web.Client/Services/WasmKnowledgeService.cs

@@ -93,6 +93,26 @@ public class WasmKnowledgeService : IKnowledgeService
         }
     }
 
+    public async Task<Result<GroundedResponseDto>> AskQuestionAsync(string question, string tenantId, Guid? ebookId = null, int limit = 5, CancellationToken cancellationToken = default)
+    {
+        try
+        {
+            var response = await _httpClient.PostAsJsonAsync("/api/knowledge/ask", new { question, tenantId, ebookId, limit }, cancellationToken);
+            if (response.IsSuccessStatusCode)
+            {
+                var result = await response.Content.ReadFromJsonAsync<GroundedResponseDto>(cancellationToken: cancellationToken);
+                return result != null ? Result.Ok(result) : Result.Fail("Failed to deserialize grounded response.");
+            }
+
+            var errorBody = await response.Content.ReadAsStringAsync(cancellationToken);
+            return Result.Fail($"Server error ({response.StatusCode}): {errorBody}");
+        }
+        catch (Exception ex)
+        {
+            return Result.Fail(new Error($"Network error: {ex.Message}").CausedBy(ex));
+        }
+    }
+
     private async Task<Result<KnowledgePacket>> CallKnowledgeApiAsync(string endpoint, string text, Guid? ebookId, CancellationToken cancellationToken)
     {
         try