Add first-class ServiceNow agent creation flow

## Summary
Provide a first-class ServiceNow setup path that wraps the existing OpenAPI/MCP action mechanics with known ServiceNow defaults and guidance.

## User Value
Tracking this as a GitHub issue moves the backlog item out of a private markdown file and gives the team a clear place to prioritize, design, implement, and validate the work.

## Proposed Behavior
Include authentication options, incident/knowledge templates, least-privilege setup, test connection, and clear naming for user/admin ServiceNow actions.

## Acceptance Criteria
- [ ] The requested behavior is designed or implemented for the relevant SimpleChat surfaces.
- [ ] Permission, configuration, and existing-feature interactions are accounted for.
- [ ] Tests, documentation, or validation notes are added as appropriate.

## Notes
- Source backlog entry: ServiceNow Agent Creation UI
- Source file: priv-simplechat-2/grouped_feature_fix_backlog.md
- Backlog status: Extension
- Current anchors: ServiceNow docs and previous OpenAPI action fixes exist under `docs/explanation/fixes/`; generic OpenAPI action support exists.
- Proposed roadmap priority: P2
- Proposed roadmap size: M