Add examples and documentation

[mtmk]

Description

Tracking issue for improving examples and documentation, as noted in #24.

Requested examples:

• Auth callout example in C# (requested in Stable release #24 by @Soundman32) — see https://natsbyexample.com/examples/auth/callout for reference
• Basic operator/account/user JWT creation workflow
• Creds file generation
• Import/export configuration

Documentation:

• XML doc comments are present on public API but higher-level guides are missing
• README could be expanded with common usage patterns