ClipboardPopover starts hidden with data-state="open" #552

• Where: clipboard_popover.rb default_attrs sets state: :open on a panel that starts hidden; clipboard_controller.js sets open in showPopover and closed in hidePopover. Snapshots clipboard/popover_*.
• Effect: the hidden panel is labelled open, unlike ContextMenu, HoverCard and Popover (closed at rest). Low user impact: the animate-in classes still run when the element is first displayed.
• Fix: state: :closed; re-record clipboard/popover_*.

Surfaced by the strict lane of the golden HTML suite (PR #548), 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 snapshots that pin it are re-recorded there with the diff reviewed.

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