`TooltipTrigger` emits a dead `variant="outline"` attribute

• Where: tooltip_trigger.rb default attrs. Snapshot tooltip/default.
  Already listed in design/v2/01-research/golden-suite.md.
• Effect: variant is not an HTML attribute and nothing in the CSS
  matches it (the data-[variant=…] selectors match data-variant); the
  outline look comes from the Button inside.
• Fix: remove it; re-record (on the 2.0 line) tooltip/*.

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.

tooltip_trigger.rb のデフォルト attrs から始めて tooltip/default snapshot を確認し、その後 design/v2/01-research/golden-suite.md をレビューします。2.0 系列では、不要になった variant attribute を削除し、tooltip/* snapshots を再記録します。完了の条件は、レビュー済みの snapshot diff にその attribute が含まれなくなることです。