Added MAC Core settings storage and schema

Property	Value
description	Added the repository-backed settings option and modular schema used by MAC Core.
version	1.0.0
type	Create
related	Settings, Extensibility

• Added the repository-backed mac_core_settings option as the canonical plugin settings store.
• Shipped the settings surface around the core, media, and utils modules.
• Added the schema-driven settings renderer so module sections and fields are defined centrally instead of in ad hoc admin-page markup.
• Added the mac_core_settings_sections extension seam so add-ons can register additional settings sections without replacing the core repository flow.