Function diffPreviewCreate

diffPreviewCreate(
kind: string,
payload: Record<string, unknown>,
): Promise<string>
Create a pending diff record and return its DiffId.

Parameters
- kind — Must be "storage_class" in v1.
- payload — JSON payload matching the schema for the given kind.
The backend returns AppError { kind: "Validation" } for unsupported kinds.

Usage
```
const diffId = await diffPreviewCreate("storage_class", {
  targets: [{ bucket: "my-bucket", key: "photos/img.jpg" }],
  current: { "photos/img.jpg": "STANDARD" },
  new_class: "GLACIER",
});
```
Parameters
- kind: string
  The diff kind string. Currently only "storage_class".
- payload: Record<string, unknown>
  The diff payload object for the given kind.
Returns Promise<string>
- Defined in src/api/diff.ts:82