Function transferUpload

transferUpload(
    profileId: string,
    bucket: string,
    key: string,
    sourcePath: string,
): Promise<string>
Initiate an upload of a local file to bucket/key.

Returns the requestId (UUID v4) immediately. The actual upload runs in a background Rust task. Listen for progress and state updates via:
```
const unlisten = await listen<TransferProgressPayload>(
  "transfer:progress",
  (event) => {
    if (event.payload.requestId === requestId) { ... }
  }
);
```
On success the backend also emits objects:updated { profileId, bucket, prefix } so the frontend can invalidate the adapter cache for the affected prefix.
Parameters
- profileId: string
  The profile whose credentials to use.
- bucket: string
  The destination bucket name.
- key: string
  The S3 object key to create or replace.
- sourcePath: string
  Local filesystem path of the file to upload.
Returns Promise<string>
The requestId to correlate progress/state events.
- Defined in src/api/transfers.ts:204