Add admin walkthroughs for common agent templates

## Summary
Add opinionated admin flows for creating common agents such as ServiceNow, Microsoft Graph, SimpleChat FAQ, and operations assistants.

## 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
Use the existing agent template gallery where possible. Templates should prefill instructions, recommended capabilities, required action type, and setup checklist while still letting admins edit details.

## 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: Admin Agent Template Walkthroughs
- Source file: priv-simplechat-2/grouped_feature_fix_backlog.md
- Backlog status: Extension
- Current anchors: `application/single_app/functions_agent_templates.py`, `application/single_app/route_backend_agent_templates.py`, `application/single_app/static/js/admin/admin_agent_templates.js`, OpenAPI/action support
- Proposed roadmap priority: P2
- Proposed roadmap size: M
- Related: #799 tracks an Action template gallery; this issue focuses on admin walkthroughs for agent templates.