Adds an N-tool for the floating card that drops from a "⋯ more"
button or appears on right-click. Emits the OPEN state: vertical
stack of padded icon+label rows in a white card with subtle stroke
and shadow. Positioning and show/hide are caller concerns (same
philosophy as add_modal_shell_v0 / add_toast_v0).
Destructive items (destructive=true) render in red with role
`action-menu-item-destructive` so renderers can style the hover
state separately. divider_before=true on any item (except first,
where it's ignored) inserts a 1px hairline above — useful for
"Edit / Share / Report / Delete" grouping patterns.
Wired through all 3 paths + parity/contract/design-prompt tests.
Handler test covers 7 cases: simple list, destructive red fill,
divider between groups, leading-divider ignored, label-only no
icon, width clamp, bogus parent_id rejection.
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