Carousel buttons have the wrong or missing screen-reader label

• Where: carousel_previous.rb renders span.sr-only "Next slide";
  carousel_next.rb renders no sr-only span at all. Snapshot
  carousel/vertical line 17.
• Effect: a screen reader announces the previous button as "Next slide"
  and the next button as unlabeled.
• Fix: "Previous slide" on the previous button, add "Next slide" to the
  next button; re-record (on the 2.0 line) carousel/*.

Surfaced by the golden HTML suite (PR #536), which pins what 1.6 renders today — this defect included. Per maintainer decision (2026-09-19) main stays as is: this is addressed on the 2.0 line, and the golden snapshot that pins it is re-recorded there with the diff reviewed.

Source: design/v2/follow-up-issues.md.

从 carousel_previous.rb 和 carousel_next.rb 开始，然后检查第 17 行的 snapshot carousel/vertical，以及 2.0 线上的其他 carousel/* golden snapshot。运行 golden HTML suite 并重新记录 carousel/*；当上一个和下一个按钮具有正确的屏幕阅读器标签，并且审查过的 snapshot diff 反映了这些标签时，即表示完成。