Add confirmationDialog (action sheet)

[colemancda]

Adds .confirmationDialog(_:isPresented:titleVisibility:message:buttons:) — a real public API, and the natural sibling of the existing .alert. Unlike an alert's two-button AlertDialog, a confirmation dialog lays out any number of choices vertically as a bottom action sheet, matching iOS.

Shape

• Mirrors the _AlertView pattern: emits a hidden ConfirmationDialog child of its content (hasConfirmationDialog flag on the parent), reusing AlertButton and its roles. Each button's callback runs the action and writes isPresented = false, so Swift stays the source of truth.
• New Visibility enum for titleVisibility (the title is hidden by default, shown when .visible, matching iOS).
• Interpreter renders it as a ModalBottomSheet: optional title/message header, then one full-width TextButton per choice, with .destructive buttons in the error color. Drag-to-dismiss calls back.

Verification

• swift test — new emission/dismissal test (asserts the flag appears on present, the destructive button carries its role, and a choice clears the flag), 68 total passing
• Emulator (Alert screen, new "Show confirmation dialog" button): the sheet presents with title "Manage item", message, and Duplicate / Share / Delete (red) / Cancel; tapping Delete fired its action and dismissed the sheet (result text → "Deleted from dialog")

Note

Like alert, the dialog is picked up when attached at the current navigation screen's root (RenderSheetsAndAlerts scans the top screen's children) — same scope as the existing alert/sheet.