Add PDF inline preview support to knowledge base viewer

frontend/src/components/KnowledgeBaseViewer.js

@@ -191,16 +191,28 @@ export default function KnowledgeBaseViewer({ article, onClose }) {
 
             {/* PDF */}
             {isPDF && (
+              <div className="w-full" style={{ height: '700px' }}>
+                <iframe
+                  src={`${API_BASE}/knowledge-base/${article.id}/content`}
+                  title={article.title}
+                  className="w-full h-full rounded"
+                  style={{
+                    border: '1px solid rgba(14, 165, 233, 0.3)',
+                    background: 'rgba(15, 23, 42, 0.8)'
+                  }}
+                >
                   <div className="text-center py-12">
                     <File className="w-16 h-16 mx-auto mb-4" style={{ color: '#EF4444' }} />
                     <p className="mb-4" style={{ color: '#94A3B8' }}>
-                  PDF Preview not available. Click the download button to view this file.
+                      Your browser doesn't support PDF preview. Click the download button to view this file.
                     </p>
                     <button onClick={handleDownload} className="intel-button intel-button-success">
                       <Download className="w-4 h-4 mr-2" />
                       Download PDF
                     </button>
                   </div>
+                </iframe>
+              </div>
             )}
 
             {/* Images */}