Refactor database configuration from config-utils into its own file

[mbg]

The config-utils module has grown extremely large, making it difficult to understand the dependencies different parts of the file have on each other. This PR moves UserConfig (i.e. the database configuration for the CLI) and associated types and functions into a new file. The same is done with corresponding tests. The various error message functions from config-utils now also live in a separate file.

There should be no change in behaviour.

Risk assessment

For internal use only. Please select the risk level of this change:

• Low risk: Changes are fully under feature flags, or have been fully tested and validated in pre-production environments and are highly observable, or are documentation or test only.

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Consider adding a changelog entry for this change.
• Confirm the readme and docs have been updated if necessary.

[Copilot]

Pull Request Overview

This PR refactors the large config-utils module by extracting database configuration-related code into separate files to improve maintainability and reduce module size. The refactoring splits user configuration types, functions, and error messages into dedicated modules while maintaining the same public API.

Key Changes

• Extracted database configuration logic to src/config/db-config.ts
• Created src/error-messages.ts for configuration error message functions
• Moved corresponding tests to src/config/db-config.test.ts

Reviewed Changes

Copilot reviewed 14 out of 15 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/error-messages.ts	New module containing error message generation functions
src/config/db-config.ts	New module with database configuration types and functions
src/config/db-config.test.ts	Tests moved from config-utils.test.ts for the extracted functionality
src/config-utils.ts	Refactored to import from new modules and re-export public API
src/config-utils.test.ts	Updated imports to use new error message module
lib/*.js	Compiled JavaScript files reflecting the TypeScript changes

[henrymercer]

I haven't taken a thorough look at all the moved code, since most of this is just moving code from one file to another, but the structure makes sense.