Central mapping from error atoms (returned by PhoenixKitCatalogue.Catalogue and the import pipeline) to translated, user-facing strings.

Keeping UI copy in one place means every "not found" / "delete failed" / "cycle" flash reads the same wording, and translations live in core's gettext backend rather than being scattered across LiveViews. Callers pattern-match on atoms (or tagged tuples for atoms with parameters); message/1 wraps each mapping in gettext/1 at the UI boundary.

Supported reason shapes

• plain atoms — :would_create_cycle, :cross_catalogue, etc.
• tagged tuples — {:referenced_by_smart_items, count}, {:duplicate_referenced_catalogue, uuid}, {:invalid_price, raw}, {:invalid_markup, raw}, {:sheet_empty, sheet}, {:sheet_read_failed, sheet, raw}, {:xlsx_open_failed, raw}, {:xlsx_read_failed, raw}, {:csv_parse_failed, raw}
• Ecto.Changeset.t() — passed through unchanged so callers can keep the changeset for <.input> rendering. UI flashes typically pull a summary via Ecto.Changeset.traverse_errors/2.
• strings — passed through unchanged (legacy / interpolated messages)
• anything else — rendered as "Unexpected error: <inspect>" so nothing silently surfaces a raw struct or tuple

Example

iex> PhoenixKitCatalogue.Errors.message(:would_create_cycle)
"Cannot move a category under itself or one of its descendants."

iex> PhoenixKitCatalogue.Errors.message({:referenced_by_smart_items, 3})
"Cannot delete: 3 smart items still reference this catalogue."