fix: admin page minor bugs

[Kallyan01]

Summary

Three small admin fixes:

• Site checkboxes are clickable again.
• No more duplicate menu items. "Settings" appeared twice and its page mounted two roots.
• REST permissions now match the menu. OneAccess endpoints require oneaccess_manage_settings (Network Admin / Brand Admin) instead of manage_options. POST /site-type still accepts manage_options while the site type is unset, so onboarding keeps working.

Testing

On a local governing site and brand site:

• The site checkboxes toggle with a real click in both modals.
• Each menu item appears once: governing shows Manage Users and Settings, brand shows Settings. A governing site with no brand sites shows only Settings. The onboarding modal still loads when the site type is unset.
• REST: an admin with the OneAccess role gets 200; a plain administrator gets 403 (on main they got 200, including /secret-key). A plain admin can still complete onboarding.

Notes

• On main, brand sites crash with a fatal error in Profile_Request, which is fixed by a4da9cd in fix: cross-site user management and auth hardening #195. Apply that commit locally to test the brand side.
• Merge fix: cross-site user management and auth hardening #195 before this PR.

Checklist

• I have read the Contribution Guidelines.
• I have read the Development Guidelines.
• I have added necessary tests to cover my changes.
• I have updated the project documentation as needed.
• My code has detailed inline documentation.
• My code is tested to the best of my abilities.
• My code passes all lints, tests, and checks.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 6.93%. Comparing base (3ac4aa6) to head (b690624).

Files with missing lines	Patch %	Lines
inc/Modules/Rest/Basic_Options_Controller.php	0.00%	5 Missing ⚠️
inc/Modules/Settings/Admin.php	0.00%	3 Missing ⚠️
inc/Modules/Rest/Abstract_REST_Controller.php	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              main    #205      +/-   ##
==========================================
+ Coverage     6.81%   6.93%   +0.11%     
+ Complexity     601     589      -12     
==========================================
  Files           20      20              
  Lines         3036    2987      -49     
==========================================
  Hits           207     207              
+ Misses        2829    2780      -49     

Flag	Coverage Δ
unit	6.93% <0.00%> (+0.11%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
inc/Modules/User/Admin.php	0.00% <ø> (ø)
inc/Modules/Rest/Abstract_REST_Controller.php	0.00% <0.00%> (ø)
inc/Modules/Settings/Admin.php	0.00% <0.00%> (ø)
inc/Modules/Rest/Basic_Options_Controller.php	0.00% <0.00%> (ø)

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