[FIX] Use correct primary key in prompt studio list count subquery (#1902)

* [FIX] Use correct primary key field in prompt count subquery

ToolStudioPrompt uses prompt_id as its primary key, not id.
Count("id") causes FieldError on the list endpoint (500).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* [FIX] Fix ruff-format implicit string concatenation

Merge adjacent f-strings into single f-string to satisfy ruff-format.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: chandrasekharan-zipstack

backend/prompt_studio/prompt_studio_core_v2/views.py

@@ -115,7 +115,7 @@ def get_queryset(self) -> QuerySet | None:
                 ToolStudioPrompt.objects.filter(tool_id=OuterRef("pk"))
                 .order_by()
                 .values("tool_id")
-                .annotate(cnt=Count("id"))
+                .annotate(cnt=Count("prompt_id"))
                 .values("cnt")
             )
             qs = qs.select_related("created_by").annotate(
@@ -1215,7 +1215,7 @@ def sync_prompts(self, request: Request, pk: Any = None) -> Response:
         sync_result = PromptStudioHelper.sync_prompts(tool, import_data, request.user)
         response_data.update(sync_result)
         response_data["message"] = (
-            f"Synced {sync_result['prompts_created']} prompts " f"into '{tool.tool_name}'"
+            f"Synced {sync_result['prompts_created']} prompts into '{tool.tool_name}'"
         )
 
         return Response(response_data, status=status.HTTP_200_OK)