feat: allow admin delegation for System monitoring page

[whoalin1]

Summary

Closes #497

The System monitoring page is read-only but required full admin. Implement IDelegatedSettings on AdminSettings (same approach as logreader) so admins can grant the page via Settings → Administration → Delegation without handing out full admin.

getAuthorizedAppConfig() is empty because this UI does not write appconfig.

Test plan

• As admin: Settings → Administration → Delegation lists System / Monitoring
• Delegate to a group; member of that group (non-admin) can open the System page
• Non-delegated users still cannot open it
• Page still loads for full admins

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AI disclosure

This PR was drafted with the help of AI coding assistants (Cursor agents / LLM-based tools), including the description. I am responsible for it and happy to rework anything that doesn't fit.

All commits carry an Assisted-by: Cursor:grok-4.7 trailer.