Merged 'Author' nodes into 'NostrUser' for unified identity tracking and social graph representation. Introduced migrations framework to handle schema changes, including retroactive updates for existing relationships and constraints. Updated tests, schema definitions, and documentation to reflect these changes.
Replaced individual environment variable access with a unified `DatabaseConfig` struct for all database backends. This centralizes configuration management, reduces redundant code, and ensures all options are documented in `app/config/config.go`. Backward compatibility is maintained with default values and retained constructors.
