fix(frontend): show backend error detail on project upload failure (#12791)

* fix(frontend): read backend error detail on project upload failure

Backend returns error payload under `detail` (FastAPI convention), but
the upload handler was reading `message`, producing an empty alert list.
Switch to `detail` with `message` and raw-error fallbacks, typed via
AxiosError.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix(frontend): simplify project upload error handler

Revert defensive AxiosError typing; keep direct `detail` read which is
sufficient for the upload error path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix(frontend): guard upload error handler against missing response

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: 2 people

src/frontend/src/components/core/folderSidebarComponent/components/sideBarFolderButtons/index.tsx

@@ -168,7 +168,10 @@ const SideBarFoldersButtonsComponent = ({
                     console.error(err);
                     setErrorData({
                       title: t("sidebar.projectUploadError"),
-                      list: [err["response"]["data"]["message"]],
+                      list: [
+                        err?.response?.data?.detail ??
+                          (err instanceof Error ? err.message : String(err)),
+                      ],
                     });
                   },
                 },