API: Settings Design

[AzorianMatt]

Complete a functional design of an application settings solution.

1. Create Pydantic model-based settings architecture that provides default values, metadata, reference keys, and feature flags for overrides and read-only modes.
2. Create SQLAlchemy ORM model for storing settings in the SQL database.
3. Create settings manager class to manage database storage and retrieval of settings data.
4. Create settings manager method for restoring defaults and adding missing settings to the database.
5. Create dev router route for triggering settings reset and missing settings load.