fix: KB procedural import — map step content to description field

Steps built by _build_procedural_tree() were stored under the "content"
key but StepDetail.tsx reads "description". Renamed the key so step
text and commands display correctly during session execution.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/api/endpoints/kb_accelerator.py

@@ -931,7 +931,7 @@ def _build_procedural_tree(nodes: list[KBImportNode]) -> dict:
             "id": content.get("original_id", str(node.id)),
             "type": step_type,
             "title": step_title,
-            "content": step_content,
+            "description": step_content,
         }
 
         # Preserve content_type if present
@@ -948,7 +948,7 @@ def _build_procedural_tree(nodes: list[KBImportNode]) -> dict:
             "id": "procedure-end",
             "type": "procedure_end",
             "title": "Procedure Complete",
-            "content": "All steps have been completed.",
+            "description": "All steps have been completed.",
         })
 
     return {