Adopt Game-Systems canonical specs: content-registry, settings #57

Game-Systems now has canonical specs for systems that were rebuilt in several projects (specs index). This repo holds a copy of 2 of them. The checklist below comes from each spec's per-copy deltas table: what this copy should adopt from the reference version, and what it should drop.

Not every item fits this project's stage. Tick what you do, and strike or close the rest.

content-registry (spec)

Entry: so-event-architecture

• Adopt: An explicit registry asset listing content by id
• Drop: Using runtime sets as the content index (they track live instances, not authored data)

settings (spec)

Entry: ui-menu-settings-template

• Adopt: A versioned file through the save pipeline instead of one registry key per option; the accessibility list
• Drop: PlayerPrefs as the store for anything beyond prototypes