Editor: macro action editor in properties panel

[jonocodes]

Design: #82. The opaque pass-through (#89) correctly round-trips macro fields through save, but there is no UI to create or edit macros from the properties panel — a user who wants a multi-step action has no way to author it in the editor.

Scope

• A macro editor alongside the existing ActionEditor for button/meter/stats widgets.
• A macro is an ordered list of steps, each with a type (key/shell/dbus/delay/terminal/url/text) and value.
• continue_on_error toggle determines whether the macro stops on the first failed step.
• Add/remove/reorder steps within the macro.
• When macro is set, the regular action is ignored (per Macros: chain multiple actions in a single widget activation #68), so the editor should make this clear.

Done when

• A user can create/edit macros from the properties panel for any supported widget kind.
• The canvas cell shows the existing 'macro' badge (already implemented).