Add cancel job button and improve jobs table UI

- Remove "All Jobs" title
- Move Status column to front of table
- Add Cancel button for in-progress jobs
- Add cancel endpoint: POST /pypi/cache/cancel/{package_name}
- Add btn-danger CSS styling

frontend/src/api.ts

@@ -794,3 +794,11 @@ export async function retryAllPyPICacheTasks(): Promise<PyPICacheRetryResponse>
   });
   return handleResponse<PyPICacheRetryResponse>(response);
 }
+
+export async function cancelPyPICacheTask(packageName: string): Promise<PyPICacheRetryResponse> {
+  const response = await fetch(`/pypi/cache/cancel/${encodeURIComponent(packageName)}`, {
+    method: 'POST',
+    credentials: 'include',
+  });
+  return handleResponse<PyPICacheRetryResponse>(response);
+}