Add ConfigurationValidationRunner with IConfigurationValidator interface for
validating required settings at startup. Includes SecureStore and LDAP validators.
Expand ConfigManager with pipeline editing UI, dialogs, and step editors.
Update documentation with config validation guidance.
Add comprehensive XML documentation (param/returns tags) across 132 source
files to improve IntelliSense and API discoverability. Include ConfigManager
design documents and implementation plans for phases 1-9.