Add API endpoints for creating & editing embed configurations

Overview

Currently, embed configurations can only be created through the web interface.

This feature request adds new REST API endpoints /v1/embed/new and `/v1/embed/{id} to allow programmatic creation and editing of embed configurations using API key authentication.

Why?

• Enables automation of embed creation
• Enables automation of embed editing
• Allows integration with external systems and scripts
• Provides a programmatic alternative to the UI-based workflow

Current Solution

Users must manually create and edit embeds through the web interface at /settings/embed-config

The endpoints will use the existing API key authentication system and follow the same patterns as other API endpoints in the system.