Add vendor opposition information for all API pages

### MDN URL

https://developer.mozilla.org/en-US/docs/Web/API/WebUSB_API

### What specific section or headline is this issue about?

_No response_

### What information was incorrect, unhelpful, or incomplete?

The WebUSB API article is missing a disclaimer about vendor opposition of the standard, which is seen on other pages such as [the fenced frame API](https://developer.mozilla.org/en-US/docs/Web/API/Fenced_frame_API) and [the shared storage API](https://developer.mozilla.org/en-US/docs/Web/API/Shared_Storage_API). The warning would be useful for developers by conveying that broad support of the standard across browsers is unlikely, and also for other browser vendors that haven't yet taken a position on the issue (assuming they're not already informed about the opposition via the appropriate sources).

### What did you expect to see?

A note card in the article with the text "Warning: This feature is currently opposed by two browser vendors. See the [Standards positions] section below for details."

### Do you have any supporting links, references, or citations?

- [Mozilla Standards Positions on WebUSB](https://mozilla.github.io/standards-positions/#webusb)
- [WebKit Standards Positions on WebUSB](https://webkit.org/standards-positions/#position-68)

### Do you have anything more you want to share?

Seems like a lot of other opposed standards also don't have this warning, such as the WebHID, Network Information, and File System APIs to name a few. Maybe there would be reason to implement an automated system for generating the warnings? Mozilla for example does already supply the data via `https://mozilla.github.io/standards-positions/merged-data.json` after all.

As a smaller note, I would recommend changing the link texts in standards positions sections from "opposes" to "opposes this specification" and from "Negative" to "\ (\): Negative" for better accessibility for screen readers. A template would help with managing these warnings without having to change each one individually, but not sure how feasible that would be on MDN.

### MDN metadata

Page report details

* Folder: `en-us/web/api/webusb_api`
* MDN URL: https://developer.mozilla.org/en-US/docs/Web/API/WebUSB_API
* GitHub URL: https://github.com/mdn/content/blob/main/files/en-us/web/api/webusb_api/index.md
* Last commit: https://github.com/mdn/content/commit/db01d0c8b4cbf8a4467b1db65e17f6724d0ce710
* Document last modified: 2025-07-12T01:26:27.000Z