Auto-select Microsoft Graph endpoints from environment settings

Summary

Reduce manual Microsoft Graph URL entry by deriving Graph base URL and authority from Azure environment/app settings where possible.

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

Preserve custom cloud override settings. Admin UI should clearly show when values are auto-selected versus manually overridden.

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: Graph Endpoint Auto-Selection
• Source file: priv-simplechat-2/grouped_feature_fix_backlog.md
• Backlog status: Extension
• Current anchors: application/single_app/config.py, application/single_app/functions_authentication.py, application/single_app/example.env
• Proposed roadmap priority: P2
• Proposed roadmap size: S