Add `url` key to the `DownloadInfo` dict returned by download keywords

@Snooz82 is already working on this.

Since Aug 6, 2026.

## Use case

`Download`, `Promise To Wait For Download` and `Get Download State` return a `DownloadInfo` dict with `saveAs`, `suggestedFilename`, `state` and `downloadID` — but not the **URL the download originated from**. Verifying that a download came from the expected URL is a common real-world assertion: as a security/regression check, or on pages where multiple links can trigger downloads and the suggested filename alone does not disambiguate them. Today there is no way to get this information; Playwright has it readily available as `download.url()` on the `Download` object the wrapper already holds.

## Proposed keyword / arguments

No new keyword and no signature change — the `DownloadInfo` dict simply gains a key:

- `url` — the URL the download originated from

```robotframework
*** Test Cases ***
Report Download Comes From Expected Endpoint
New Context acceptDownloads=True
New Page ${TEST_APP_URL}
${dl_promise}= Promise To Wait For Download saveAs=${OUTPUT_DIR}/report.pdf
Click id=download-report
${file}= Wait For ${dl_promise}
Should Contain ${file.url} /api/reports/
Should Be Equal ${file.state} finished
```

## Playwright API

[`download.url`](https://playwright.dev/docs/api/class-download#download-url) — returns the URL of the downloaded file.

## Implementation notes

- `node/playwright-wrapper`: include `download.url()` in the serialized download info wherever `DownloadInfo` responses are built (the `Download` object is already in hand at those points). No new proto RPC; at most an added field in the existing JSON payload.
- `Browser/utils/data_types.py`: add `url` to the `DownloadInfo` TypedDict and its documentation table.
- `Browser/keywords`: keyword docs of `Download`, `Promise To Wait For Download`, `Get Download State` mention the new key.
- atest: assert the `url` key against the test app's download endpoint.

## Backwards compatibility

Fully additive: no signature changes, only a new key in the returned dict. Existing suites reading `saveAs`, `suggestedFilename`, `state` or `downloadID` are unaffected.