Increase topK default to 40 for multi-hop context

- Update default topK from 20 to 40 in query parameters
- Support richer context with multi-hop graph traversal
- Maintain flexible topK range (1-50) via slider
- Respect user selection of query mode (don't force mode changes)

Higher topK allows more edges from multi-hop paths to be included
in the context provided to the LLM for answer generation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

nvidia/txt2kg/assets/frontend/components/rag-query.tsx

@@ -39,7 +39,7 @@ export function RagQuery({
     kNeighbors: 4096,
     fanout: 400,
     numHops: 2,
-    topK: 5,
+    topK: 40,  // Increased to 40 for multi-hop paths (was 20, originally 5)
     useVectorSearch: false,
     usePureRag: false,
     queryMode: 'traditional'
@@ -327,7 +327,7 @@ export function RagQuery({
                 <input
                   type="range"
                   min="1"
-                  max="20"
+                  max="50"
                   step="1"
                   value={params.topK}
                   onChange={(e) => updateParam('topK', parseInt(e.target.value))}