Add Open/View action for Custom Pages in Admin Settings

[paullizer]

Summary

Add an Open/View action in the Admin Settings Custom Pages table so admins can jump directly to a configured custom page.

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

Respect enabled/disabled state, .html alias behavior, and access-level authorization. Disabled/unpublished pages can show a disabled action with tooltip copy.

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: Custom Pages Open URL Action
• Source file: priv-simplechat-2/grouped_feature_fix_backlog.md
• Backlog status: Extension, Small
• Current anchors: docs/explanation/features/CUSTOM_PAGES.md, application/single_app/route_custom_pages.py, application/single_app/templates/admin_settings.html
• Proposed roadmap priority: P2
• Proposed roadmap size: S

[paullizer]

Implemented in PR #1131: Add Custom Pages open action. The PR adds the Admin Settings Open action, updates coverage/docs, and includes targeted validation details.