Mini-CMS for app help texts

[yepzdk]

Description

Add a simple content management entity (e.g., ContentPage or HelpText) with a CRUD controller in admin and an API endpoint, so app help texts can be managed without code changes.

Considerations

• Needs discussion on scope and content structure
• Should define what fields are needed (title, body, slug/key, locale?)
• Determine whether rich text editing is needed
• API endpoint design for the app to consume

Part of #35