feat: Day 21-22 - knowledge base frontend completed, fix CORS and file upload issues

- Complete knowledge base list and detail pages
- Complete document upload component
- Fix CORS config (add PUT/DELETE method support)
- Fix file upload issues (disabled state and beforeUpload return value)
- Add detailed debug logs (cleaned up)
- Create Day 21-22 completion summary document

frontend/src/stores/useKnowledgeBaseStore.ts

@@ -215,3 +215,4 @@ export const useKnowledgeBaseStore = create<KnowledgeBaseState>((set, get) => ({
   },
 }));
 
+