Add development mock analytics connections

[thebuilder]

Summary

• Add development-only mock analytics scenarios for deterministic dashboards without Vercel access
• Route mock connections through the settings UI, validation, API contracts, and backend registry/runtime
• Update documentation and tests to cover mock connection creation and validation behavior

Testing

• Added/updated client and backend unit tests for mock scenario validation and settings handling
• Updated settings dashboard tests to verify mock connections can be created and rendered in Development