Introduced a `test_default` method to `Config` to provide sane defaults
for integration tests. This refactors several test files to use this new
method, reducing boilerplate and improving maintainability.
Added `LLM_TIMEOUT_SECONDS` to the environment variables and `Config`
struct.
Introduces a new `config` module for loading application settings from
environment variables and a `users.toml` file. An `error` module is
added to handle application-specific errors gracefully. An
`.env.example` file is created to show available configuration options,
and `users.toml.example` provides a template for user data. The main
function now initializes the configuration and prints the server port.
Brummel