Python Configuration

Solid foundation for externalizing Python app configuration using pydantic-settings and environment variables. Sets up typed configuration classes that validate at startup and fail fast with clear error messages when required values are missing. Covers the essentials: structured settings with sensible local defaults, secret management, environment-specific behavior, and type coercion for booleans and lists. The nested configuration pattern using double underscores is clean for organizing complex apps. Most importantly, it enforces the twelve-factor principle of keeping config separate from code so you can deploy the same codebase across environments without modification.